Booking Trains???

I booked our train tickets from Amsterdam to London and back on http://www.nshispeed.nl/en and got a good rate. Just one ticket gets you from any station in Holland to London via Thalys and Eurostar.

Don't use RailEurope for the northern portion of your trip (I have almost no knowledge of how Trenitalia works, so I'll let others comment). For Brussels to Amsterdam, you have two options. If you want the high speed Thalys line, go to:
http://www.thalys.com/de/de/?time=1307861248 The sooner you book, the cheaper, although the downside is that you must commit to a specific train. If you want to ride the slower, cheaper option, just buy tickets for the regular intercity service the day you want to travel. Trains leave hourly. Over the station loudspeaker, they will refer to this as "the international train to Amsterdam", so you don't confuse it with Thalys. For Brussels to Bruges, buy your ticket right before you get on the train. No discounts for advanced purchase and at least two or more trains leave every hour. For Amsterdam to Paris, Thalys can take you all the way, or you can take a much longer series of intercity trains.

Thanks for all the advice. If I wanted to take the local cheaper train from Brussels to Amsterdam. Do you think I should buy this in advance or should I buy it the day of at the station?

For the regional train, buy same day for maximum flexibility.

There's no advantage to purchasing tickets in advance for the IC train Brussels to Amsterdam. Seat reservations aren't allowed and there are no advance purchase discounts.....just one fare. Purchase the tickets at the station on the day of your journey.

Thanks a lot for all the help, I really appreciate it. Also for the eurostar train from London to Brussels, that I should book in advanced correct?

"Also for the eurostar train from London to Brussels, that I should book in advanced correct?" Yes. The further in advance, the better the discount. You can book 4 months out.

And just to kick it to death, book that London > Brussels ASAP; I just 'helped' help someone today who could've paid less for her family of four than HER ticket is going to cost - OUCH. Go to http://www.trenitalia.com/ for your Italian trains; click on the English flag at the top center of the page. You can save alot with their MINI fares; it depends on how far in advance you purchase them. Of course, you can't return/exchange them, for the most part...Some routes (the shorter, less popular ones) don't even offer them, so just get your tickets there for those routes. See the great website from Ron In Rome for all the info you'll need for buying those tickets: http://www.roninrome.com/transportation/buying-train-tickets-updated

So here are your trains and what I recommend you to do: Roma to Montessero al Mare => buy in advance from Trenitalia website a Roma - La Spezia ticket for IC or ES trains, where advanced purchase discounts + reservations are required/available. For La Spezia - Montessoro ticket, buy it when you arrive in Italy in any Trenitalia ticket machine: no reservation is possible and the price is fixed for the last hop
Montessero to Firenze => regional trains, no advance purchase possible, fixed prices. Buy on Italy. Firenze to Venezia => travel on a high-speed Frecciabianca (ES*AV) train. Buy in advance from Trenitalia website. London to Brussels => buy in advance for deep discounts. Try Eurostar and TGV websites, prices might differ a lot for the same trains. Brussels to Amsterdam => although there is a regional train, its fixed far is higher than the most discounted fares (€ 25) available for advance purchase on the Thalys high-speed train that takes 1h20 LESS than the regional trains. Brussels to Bruge (day trip) => buy in Belgium, regional train, fixed fare, no reservation possible. Amsterdam to Paris => buy in advance for deep discounts on Thalys website.