1. very important. They do not like being fully charged or over discharged. Reduced life will result.
2. You can keep them charged for up to a week without any 'Major' damage, but no more than a couple of days is ideal.
3. Yes, and this is a bad thing. This is due to the IR of the pack and the higher the IR, the faster they will self discharge. If you are noticing this, completely discharge the pack and toss it.
4. A little swelling is not that big of a deal. Not in my opinion anyway. If a pack gets warm, it will slightly puff. Excessive puffing though, see #3...
5. If you overheat a pack bad enough, have a crash or compress the cells so the two elements touch, they will catch fire. Slight puff I'm not worried about, but anything more and again, see #3.