Hi, 2 friends and I are flying from ORD to PRG via JFK on Delta on a Wednesday. We have an 8 hour layover. We are planning on NO Checked baggage. Via other posts, I'm pretty sure we can get to Manhattan for a few hours. 2 of us have been to NYC in last 4-5 years so we don't need to do too much touristy stuff, like ESB or Statue of Liberty (which based on research, I don't think we'll have time for anyway.

I was thinking of Central Park and it's environs as 2 of the 3 are big Beatles fans and I could show them the Dakota and Strawberry Fields. Some museum has Ringo's gold drumset, but I don't know if paying admission just to see that (1hr/2hr's there) is worth it.
1. Our flight out to PRG is scheduled at 5:20pm. When should we be back to JFK? Do we need to allow the "recommended" 3 hours?
2. Would it be better/worse if we had checked bags?
3. I think, based on my research, that we can store our bags by the train. But could someone confirm that? Or should we just take them with us?
4. Any good deli's around the area of Central Park?

thanks much.