I'm a newbie myself, but think I can answer some of your basic questions - I won't make any specific brand recommendations because I just don't know at this point (lack of experience).

Point 1 - I have seen MANY .12, .15 and .17 engines for around 100$, but from what I've gathered over the past several months you won't be getting a race engine for that price (200$+ generally).

Point 2 - You will need to buy a pipe and header separately, usually the LHS or shop you buy from will be able to tell you what you need based on the engine you own or are buying.

Point 3 - Boiling it down, you need a way to heat the glow plug before turning over the engine. You can do this with a glow starter or the panel on the front of a starter box with leads. Once the glow plug is 'glowing' you can start turning the motor over expecting it to fire. This can be accomplished with a starter box - it engages the flywheel, hence cranking the engine.

Point 4 - The typical nitro car will run around 12+ minutes, at least from what I've experienced just bashing around.

Keep hanging out here and asking questions. There's quite a few knowledgeable members that will probably do way better than me at answering your questions.

Also, check out the R/C magazines' web sites (do a search) for other tips and tricks.

Have fun,
SlingItX