MichelZ - I am stuborn and go after niches no matter what! I started a gadget site in Jan. gadgets like laptops cellphones etc. are huge comp. but I get good traffic to them. I don't think comp matters, build a good site and you will be ok! start the site out with pages that hit the long tail and get back links@
I use the SEOmoz keyword difficulty tool for this. It should give you a pretty good idea of how difficult it will be to rank for a certain keyword or keyword phrase. The reports do take a while to run (30-60 minutes), but the information is worth the wait.