Replying to Getting into longboarding... questions

so i know the companies like sector 9 and arbor and thats about it.. but other than that, i dont really know what are some other legit companies..

i'm looking at buying a used board to get me started and move up from there.

but what are some things i should know?
or recommend me a board.. from the riding i've done, i like a fair amount of flex, and medium to long length. if i had to guess, like 3-ish feet?..its been a while..

is there a rating system for flex?
how do they measure they're boards? inches?
whats considered long or medium?

and lastly, what are good trucks/wheels?

thanks +k for help

if you're selling one, hit me up