Prozak,
 
I was in your position last year travelling over from Ireland and I'd recommend staying on site in the tangerine fields. The money you're going to spend on B&Bs and transport should cover one of the pods or a ready made tent. The area they're in is separate to the main camping site and has its own showers, hot water etc facilities. We stayed in a myhab http://www.myhab.com// (don't appear to be here for this year :-() and really enjoyed it. We'd contemplated doing what you're planning and I can tell you I'm glad we didn't as I'd say we'd have gotten fed up travelling between the festival and Lowestoft.
 
We're coming back this year and will be staying on site again as it was great - very helpful and friendly staff and "neighbours" and a nice area to chill out in during the day, found it nice to get away from the action at times and have a little siesta to boost energy reserves for the late night partying :-)
 
For what it's worth and to give you something to think about this was our itinerary last year (we made a bit of a holiday out of it.)
Wed: morning flew to Stansted and then train from airport to Cambridge (only about 30 mins away) Stayed there for a night, relaxed, picked up some festival essentials in the shops and really enjoyed the city.
Thurs: evening train from Cambridge to Ipswich and then bus on to festival site
Thurs - Sun night: Partyed.
Mon: Once we'd "checked out" of campsite we headed to Lowestoft for some recovery by the sea, stayed in a B&B and just chilled out.
Tues: Train to London for a night and then flew home on Wed.