Right, the forking problem doesn't affect rewards. I had been staking on a fork a couple days ago before I decided to go offline until the fix was released. Since the fix was released earlier today, those rewards have been rolled back and replaced by new rewards from a block I staked today. So no problem at all. Even transactions should get rolled back with no loss (Please avoid doing this though.)
Staking with a small balance is not going to help the network much. So don't feel like you have an obligation :) It's true it would be nice to stake a block every now and then to earn interest, but again, with so few coins the odds are pretty small. I wouldn't worry about this aspect of things until you've built up a balance :)
*And yes, interest rewards do build up even when your wallet is offline. (I will note, however, this feature may change in the coming year to encourage people to keep their wallets online more frequently.)