Mandelbrot

so , 2 questions...

Im looking to get likely a raleigh or schwinn first off, $2-300-something range while I get a feel for this again and to minimize the potential trauma of more vanadalizm or theft untill I have assessed the security situation at my new job.
virtually nothing I have looked at has 100% what Im looking for as far as features...
so.... how is the parts compatibility between bikes in the US market?

I would ideally also like to get together a second backup/guest bike to have on-hand building from parts (since I like to tinker anyways) or else turn the 1st into that after getting a better/lighter frame in the future.
these are all theoretical plans but i assume this is somewhat possible since there are so many frames and parts on ebay.

also it would seem that models one-year old are signifcantly cheaper (even new) than
this years...is there a good place (besides maybe ebay) to find 09, 08 or 07 models new?
those seem hard to find so far and I, just on principle, would not want to pay an extra cent
just to say "its this years model" for another 5 months.