stance needs to get good society
So, big explanation times. the link below is what a cheat 900 should look like.
http://www.club540.com/assets/video/.../cheat-900.mp4
I'll explain some of your confusion about the total degree rotation. It's called a cheat because the setup contribute 180° to the total revolution. then, in a cheat 900, you spin 540° in air, and then you kick outwards (NOT A HOOK KICK). the final 180° comes from your landing. So, in the end, you have:
180° + 540° + 180° = 900°
now in a cheat 720, you perform a hook kick after 360° in the air, and *drumroll* 180° + 360° + 180° = 720°
so thats how the degrees work.
cheats consist of both hook kicks and round kicks, as you see above, 720 = hook, 900 = round, 1080 = hook, 1260 = round, 1440 = hook.
now landing, you want the leg to be fully extended like you said and im including a replay of shoddy doing a clean ass tricking sequence in mp (theres a cheat 900 at the start). so hopefully that should help you with the landing.
while launching you dont want to contract or extend your pecs too much because it makes hard to keep your momentum since you have to readjust your pecs too much.
almost as soon as you hit air you want to start tucking in, it gives you the most rotation, from what ive seen.
for it to be a proper cheat trick it has to have either a hook or a round depending on how many degrees you spin, but if you dont kick i guess its just a cheat setup.
when you kick, you should tilt a little and dont use your chest for the kick.
also, the best website to find information about tricks is club540, they have literally everything with detailed explanations and video of the trick being executed.
have fun cheating!