You can use your Season Pass parking at both parks in the same day...the same applies if you pay the $25 daily parking fee, you would just have to show your receipt.
As far a I know, King Cobra is the only ride where they actually weigh you before entering to make sure. If the others do have a weight limit, it's on the honor system.
If you do end up going to SFGA, you can buy a Thrill Pass online for the same prices as the gate admissions prices ($67.99 + tax) - you'll get your card at the front gate and be done, and you can use up until 9/13 if you do make another trip this summer.