the more the advace the more bottm end your going to have , but only thing with static unlike electronic curves (like a dyna) is its only set for top or bottom the entire ride...
get a dyna and your curve will change thoughout the rpm ranges to advance or retard your timing for better all around performance. plus you can get the software and make your own curves, downfall is you should do it on a dyno to get it right so you can see where your faults are in the programming and fix them to gain max hp from it.
it depends on what your compression is, more then likey you will be ok with +7 but only way to be 100% sure is do a compression test . +4 without a dought youll be fine doing...
get a plate the keys are prone to shearing off and throwing your crank out of true, also you cant make changes to your timeing without pulling the flywheel and changing your key... the plate can be chaned by lossening 3 screws... if your going to do it . do it right the first time.
i got mine at sears... i want to say it was 60 bucks.. only thing i dont like about it is the threads need to have a hex head so you can screw it in using a wrench... instead you have to use a set of pliers and it gouges the shit out of your tool..