I-Drive down that far should not be horrible (south of Sea World is generally OK).
To get to Disney, continue south on I-Drive to World Drive, then turn right.
In terms of off-site restaurants, I would stick to 535, avoid anything near the Convention Center. (To get to 535, simply turn right on Apopka Vineland Road, athe Publix and Walgreens, and continue to the stop light). But a lot of places on I-Drive has a counterpart on 535 (Bahama Breeze, Fridays, Golden Corral), so it should not be much of a problem.