First time in Europe! Many more to come.

Considering that Manchester United FC is not doing so well, you might consider going to the Etihad stadium of Manchester City F.C. instead of Old Trafford.
I wouldn't waste a precious day in Paris to visit EuroDisney. I would leave Disney parks for another trip closer to home. If you come from Singapore, I think there are parks in Hong Kong, Shanghai and Tokyo. Or you can leave that for your next trip to Orlando, Florida or Anaheim, California (neither city has anything else worthwhile to see)
If you skip EuroDisney, then 4 nights in Paris (3 full days) can be more acceptable than just 2, which are definitely not enough.

Pisa can be visited in one hour or two (there is only one square to see, where the Cathedral, Baptistery and leaning tower are). Then you can proceed to Cinque Terre and spend your nights there. 2 nights at the Cinque Terre is all you need, although others may disagree. However compared to what it was when I used to go there every year 30+ years ago, the place has become a zoo overrun by tourists like Disneyland (so another reason to ditch Eurodisney).

Florence 4 nights is good, because that gives you 3 full days, and in one of those 3 days you can easily take a day trip to some other Tuscan town (like Siena, San Gimignano, or hundreds more to choose from).

I think Rome can be decreased by one night, which you could add elsewhere (Paris comes to mind). If you stay in Rome 5 nights, you should take advantage of a day trip out of town for one day (Orvieto or Naples/Pompeii or Tivoli or Ostia Antica)

Assume you are visiting family/friends in Old Trafford. A bit of logistics to get there from Heathrow. You may be very jet lagged after 18 hours traveling from Singapore and then 2 trains plus 2 Metro/Subway legs may be a bit trying.
I think you need to up your daily budget. When you include train tickets, lodging, food, and sights like museums, 80 euro per person is light. I'd up that at least 50%.
But I am envious of your flight costs.

Edit- If you do want to start in Manchester, why not book into there using Emirates with a connection in Dubai. Looks to be the same cost or less.

I'll second Roberto's recommendations. Between London, Paris, and Rome, Rome is not the city that I would give the extra day to.

Another yes vote for Roberto's sound advice.

If you skip the CT, you could add time to London and/or Paris. Or fly from Paris to Venice (3 nights, taking 1 from Rome). You could visit Pisa (not much really) in a 1/2 day trip from Florence.

And yet another vote for Roberto's always great advice. I also agree with Sam in terms of travelling to Manchester on your arrival day. That's going to be a brutal and exhausting trip after a long international flight. My suggestion would be to skip that and spend your first five nights in London.

I'm also wondering about your "Pisa day trip". Are you planning to spend some time in Pisa after arrival there, or go directly to the Cinque Terre?

Ditto to Roberto's comments. Recommend a day trip to Siena while in Florence.

Lots of great logistical advice above. As to your budget, I agree it is light. The only way to be certain is to plot out in a spreadsheet what the actual costs are. List every sight you plan to see and its cost. Look at passes that might save you money on museums (Paris Musuem Pass for example). List your specific AirBnB or VRBO or whatever-sourced lodging. Estimate meal costs. Will you picnic for lunch? Cook dinner in? Cooking takes time away from sightseeing and enjoying the culture, but if you have a kitchen a couple of simple cooked meals a week will save some money. Also, list your trains/buses as an estimate and look into money-saving transit passes such as buying a carnet in Paris, an Oyster Card in London. Rick Steves' guides have a lot of good budget-planning tips. It's a lot of work to do this degree of planning, but it gives you a foundation for your trip and minimizes surprises.

Getting an apartment/studio apartment with a clothes washer is very worthwhile so you can do laundry easily and cheaply.

A vote for Roberto yet again.
Paris is fabulous. Take time to walk the 4th and 5th. Get fresh baguettes, cheese and wine. Visit Jewish deli in the Marais. So so good! Go to an outdoor cafe. See the Eiffel tower at night. Sure I am glad I saw Mona, but I will never forget the afternoon my husband, friends and i took a warm baguette and a bottle of wine down to the Seine and watched boats go by. These are priceless things that I think about as I get older.

The Leaning Tower of Pisa was closed when we were there in 1999 but was awesome to see nonetheless. As was Piazza dei Miracoli..

We stayed in Corniglia in the CT and really loved it. It was such fun to take boat to the other villages. The fresh anchovies and Sciacchetra is forever on my mind!

Ahhh Firenza!!! What marvels she holds. David.
My favorite art treasure. Beyond compare.
Prepare for the Duomo. No picture does her justice. Massive.
Uffizi ..magnificent and not to be miss. Botticelli !! I bow to you.
Baptisty doors are a truly from paradise.

Mi Roma..
Campo di Fiori
Trastevere
Piazza Navonna
Pantheon
Trevi Fountain
Colosseum
Spanish steps
In my opinion if you see these you have seen the best of the best!!
One thing I truly loved and remember is the evening Passeggiata. We walked with locals and felt part of the neighborhood.

In Europe in general we stay in apt instead of hotels. It is cheaper, it is bigger space, and you become a local!

I am a firm believer that one should be culturally sensitive and respectful whilst travelling. Disneyland, just like MacDonalds, is best visited in California or Florida.

I am a firm believer that one should be culturally sensitive and respectful whilst travelling. Disneyland, just like MacDonalds, is best visited in California or Florida.

Brilliant, David!

thank you guys so much your great feedbacks!

Roberto, the city of manchester will always be red :)

as i'm planning in advance, my intention is to watch a live game in old trafford but the football match fixture for next season will not be out till end May or June. so its not wise to fly to manchester, i can only confirm my schedule for the London leg nearing then. but i'll be definitely visit the stadium at least.

as for disneyland, seems like the general feedbacks for us is to give it a missed. i guess we will be queuing and waiting for the rides most of the time there?

for pisa. it will be a few hours visit of the square and probably a lunch there before heading to CT.

for rome, we would probably squeeze in a day to visit pompeii. and the attractions that cunamnt mentioned in Rome are more or less what i'm planning to do. how many days would you guys reckon it may take?

lastly, i guess we will have to our budget a little more and also detailed out the fixed expenses.

Campo di Fiori
Trastevere
Piazza Navonna
Pantheon
Trevi Fountain
Colosseum
Spanish steps

Above are the items "cunamnt" listed for Roma. Some are walk-bys: Piazza Navona, Trevi, Spanish Steps. Pantheon takes 30-60 minutes depending on how detailed you are. Colosseo & surrounding sites, the Palatine Hill and Forum, takes 1/2 day for all. Trastevere is a part of town. You can spend days there or 1/2 a day. But what about the Vatican Museums, St. Peter's Basilica, The Galleria Borghese, and all the other museums and churches filled with art? You will have to make a list. You can EASILY pass 4 full days, meaning 5 nights, in Roma, with full days but some time for just wandering and taking the passeggiata. Note some sites have closure days so do not, for example, plan the Vatican Museums for a Sunday. Rick Steves' Rome Guide has a great day-by-day plan that could help you make the most of your time. His guidance on how to plan a trip is priceless, too.

Now I understand the Old Trafford connection. That is a fast train from Euston Station to Manchester Picadilly, then Northern Line direct to the stadium on game days.
Hey, if you want to go to Disneyland, its your vacation. Better there than Man U (I'm partial to AC Milan)

We are big Disney fans - my husband visited Disney Paris a few years ago when he was stuck in Paris for business over a weekend. If you want to take a day out to see it, then you should.

However, I have made 3 trips to Europe so far (2 with my kids) and we have not yet made it to Disney Paris. Too many other things to see. I will go at some point though, because my husband said it is really pretty there and very well done. On you first trip though, I would not consider it high on the priority list unless you are a really big Disney fan and want to go kind of for comparison sake, to see the similarities and differences with the other parks. Plus that will seriously kill your budget. :)

I would be inclined to see Pisa as a day trip from Florence, skip the Cinque Terre, and add Venice instead.... :) You are smart to base most places 4 nights or so... our first trip we whipped around Italy so fast I hated it. No travel boards back then to warn me! Live and learn....

Have a great trip!
Kim