there used to be a really great program, called market samurai, to find key words, etc. by an australian company. but unfortunately, they discontinued it. pity. there are some really great key word research tools available for free on the internet. its best to always find 1st relevant key words to your niche. but once you have found all the relevant key words to your niche, you can start using more general / broader key words. even thou its important to use relevant key words, its not a bad idea to use key words that have a general meaning as well. seo has become an art & a science at the same time.
the longer you own a domain also influences in its ranking. so think long term if your really serious about creating a successful web page orientated business. also, its better to buy a domain name for as long as you can, normally 5 yrs is the max, if i remember correctly. that can also give a positive seo ranking. it shows that you are committed for the long run.