Depends how long his contract was initially.
If it was a 6 year contract with 600k bonus and you trade him with 3 years left, it would cost you 300k (600k/6= 100k.... 100k*3= 300k pen) off you cap next year.
If it was a 4 year contract (600k/4= 150k... 150k*3= 450k penalty.)
If it was a 3 year contract (600k/3= 200k...200k*3= 600k penalty.)
As you can see, it all depends on how long the contract was initially.
The best way to know the exact penalty amount is to try to release the player and before you confirm the release, an info box appears telling you how much cap pen it'll cost you (don't confirm release obviously... just see the amount.)... this number is the same if you trade a player.
The cap room is available immediately but you will be penalised the penalty amount next year.
2)
I'm pretty sure preseason doesn't count towards gametime, purely because preseason stats aren't recorded in a players season profile so i'd assume the progression formula won't have access to it.
I've found that "number of plays played in" is as important as actual season statistics (TD'S, yards....). You can find it in the player season stats area... use the back buttons to scroll to it.