7 days Switzerland from Milan

Some comments.

Day 2: It is the Bernina pass line. Bad spellings mean you can't find things on the internet! The Bernina Express is an extra tourist train on the route, but there are other hourly trains as well.

Day 3 etc: Most people recommend staying somewhere further into the mountains than Interlaken. For example, Mürren, Lauterbrunnen, Wengen or Grindelwald. This map of the area may help: http://www.regionalpass-berneroberland.ch/assets/karte-und-partner/Regionalpass-Panoramakarte-2017.pdf

Day 6 etc: I would recommend Luzern (local spelling) over Arth. Luzern has more tourist facilities. It has a nice old town, lake boats (Arth is on a different smaller lake) and is the starting point for going up Titlis.

Luzern to Rome is a long trip, and you should consider a cheap flight from Zürich. By train it is only 70 minutes from Luzern to Zürich airport.

Thanks for the reply.
Luzern to Milan/Rome, I wanted to pass through the Gotthard Base tunnel, hence the train.

A couple more questions

1. For Interlaken and surroundings, my question was that if I choose some place like Murren or Wengen, would that add a lot of logistical complexity? Also, given that these villages are smaller, will all the tourist infra be functioning in early May?

2. Does it make sense to go to mount Titlis after seeing Jungfrau

3. Is Bern worth a day visit considering I will have to give up one day in the mountains? I know this is subjective, but just wanted to hear some opinions.

If you read about the train changes from Interlaken Ost to Murren you'll be highly intimidated. Until you arrive and see that those changes get smaller and smaller and finally just involves stepping out of the gondola, walking 15 steps, and stepping onto the little train onto Murren. Don't waste your time in Interlaken when you're so very close to amazing scenery and alpine villages like you've never experienced.

End of May means that not every hotel will be open. But Murren is a living village - with REAL people who live there and require all of the infrastructure that you as a tourist could need. Transport, Grocery Store, Restaurants, ATM - all there and providing services year round.

1) For Interlaken and surroundings, my question was that if I choose some place like Murren or Wengen, would that add a lot of logistical complexity? Also, given that these villages are smaller, will all the tourist infra be functioning in early May?

Not really, they are about 30 minutes (Lauterbrunnen, Grindelwald) to 50 minutes (Mürren) from Interlaken, and there are 2 trains per hour (red lines = train on the map I linked to last time). I suspect if you stayed in Interlaken you would be doing the same trip every day to get higher up into the mountains. By staying in these places you save the "commute" and get to see better views as soon as you wake up.

2) Does it make sense to go to mount Titlis after seeing Jungfrau

Not really. But only do either if the weather is clear. Check the weather and make a decision in the morning. It can llok lioke harmless high cloud down in the valley, but at the summit you are in the middle of that cloud.

3) Is Bern worth a day visit considering I will have to give up one day in the mountains? I know this is subjective, but just wanted to hear some opinions.

Probably not, if you are time-limited. Bern is a nice city and may provide a nice change.

I will have a Swiss pass for the trip, but I guess it does not cover the Eurocity trains to Milan. Do I have to book this train early given that prices are not standard and seem to go up based on demand?

I will have a Swiss pass for the trip, but I guess it does not cover the Eurocity trains to Milan. Do I have to book this train early

Your Swiss pass will cover you up to the border interchange station between the Swiss and Italian railway companies (provided your pass is still valid on that day). If travelling from Luzern via Arth-Goldau to Milan, that station is Chiasso.
You can see this in the map here: https://www.sbb.ch/content/dam/infrastruktur/trafimage/karten/karte-sts-pass-gueltigkeit.pdf
it is where the colour changes from red (pass valid) to grey (non-Swiss line, pass invalid).

You need to go to the Italian railways site: http://www.trenitalia.com/tcom-en and buy a ticket from Chiasso to Rome. This will include the train from Switzerland to Milan and the one from there to Rome.
The earlier you buy the ticket the cheaper it will be. But Italian tickets (unlike Swiss ) are specific to a train, so you will need to decide which train you want to travel on. You do not have to get off the train at Chiasso. Just make sure when you get on the train at Luzern or Arth-Goldau, you are on the train for which you have a ticket from Chiasso.

Thanks a lot for your replies.
I thought the EC trains needed reservations before boarding, but when searching on sbb.ch upto Chiasso it did not show the reservation required sign.

So as I understand, I just need to buy the Chiasso- Rome leg without bothering about the Swiss part. I can just board the Eurocity train and sit anywhere ( with a valid swiss pass) upto Chiasso.

The EC train needs reservations when it is in Italy, but not when it is in Switzerland. Different railway company, different rules.
Very very few trains require reservations in Switzerland (just the 4 named extra tourist trains). When you buy the ticket from Chiasso, it will automatically include reserved seats for the two trains (Chiasso-Milan and Milan-Rome).

"I just need to buy the Chiasso- Rome leg without bothering about the Swiss part." - correct.
"I can just board the Eurocity train and sit anywhere (with a valid swiss pass) upto Chiasso." - but it makes sense to sit in the seat which is on your ticket from Chiasso. Then you don't have to change seats at Chiasso.

Awesome!! All doubts cleared and Chiasso - Rome tickets booked, though I booked separate tickets to avoid any rush at Milan.

Thanks for the help.