ok peeps lemme try to answer some questions.
i'm at roughly 80% myself..
you unlock other cities by completing story missions.
a note on the schools, there arecar,bike,boat,air training schools, 1 located in each city, and they will become available thru certain missions.
the air school is located in the desert to the west of las venturas. you will do a mission in which you need to complete the flight school, and that is how it is unlocked, once you complete ALL flight school missions you can access ALL airports.
to lose any amount of stars you can hit a spray shop, save at any save location, or change part or all of your outfit.
do unlock dual pistols and dual micro smgs you need to get that weapon, and practice with it(kill people) to raise your weapon skill, once it's at 100% you get hitman skill, dual pistols, dual smg.
with other guns, machine gun, shotguns, you will reload faster, straif faster, and will be able to shoot while walking.
once you earn enough respect, and take over gang territory you can recruit up to 7 gang members to follow you(much like y our body guards in vice city) but these dudes will actually protect you, and do drive bys with you.
once you get the airstrip purchased, you will have a ww2 fighter jet that spawns there, and after some more missions(sorry, no spoilers) you get a jetpack and a fighter jet, as well as a huge chopper.
hope that helps, and hope it doesn't spoil toooooo much of it for you all.
p.s. anyone who beat gta 3 and gta vice city will recognize some characters in san andreas
nuff said, go beat it for yourself like me.