http://www.gov.im/tourism/motorsport/bike/futurett.xml

So-called "fastcraft" ferry you from Liverpool, but it is worth looking early at air-fares (Manx2.com, Easy Jet and Flybe).

I recommend Homestay in the Douglas/Braddan area. Lots of interesting spectating within walking distance and if you book your Homestay early you should have a good choice of reasonably priced accommodation.
http://www.visitisleofman.com/homestay/

Public transport links and timings are pretty good (but not as good as when the steam railway ran close to the TT Course all the way to Peel and Ramsey) and could get you out to spectate anywhere quite easily.