Well, it is pretty darned big, with LOTS of seating, and if for some reason it were jammed (and I really do NOT think it will be), you could always take your food out with you to eat somewhere outside. It seems to be that most people either eat at a table service restaurant just before the party starts, or arrive having already eaten -- once the party starts, I believe you'll find it pretty easy to grab a bite. Good luck, and have a GREAT time -- I'm sure you'll love it.
As for characters, just ask a CM when you arrive about where the characters are posted for that evening (and which ones are there). It's pretty controlled (you get into a line, and a CM assists every character in getting guests up to and then away from the character). Just have a good, solid pen ready, have it open, have your autograph book opened to the page you want signed, and you're good to go! Toon town, esp. Mickey's Judges Tent, is always a reliable place to go for characters.
This will be our 5th year attending MNSSHP. We have eaten at Cosmic Rays for the last 4 years. There has just been a handful of us in there eating. Don't know if we just happen to pick the right time or if it is like that the whole night. We were eating around 7:00 - 7:30.