Charging again overnight for a fully charged, but not used for a week, battery?

You probably don't need the 2nd charging to be overnight. But it shouldn't hurt.

As a beginner, what you really need to do if you figure you'll be in this hobby for awhile, is to plan to get an intelligent charger someday. The ones that tell you how much charge the did to bring the pack to capacity will teach you about everything anyone needs to know about their specific batteries and a lot about batteries in general. They also spot batteries that're bad or going bad. Wallwarts don't do that for you.

Also, beginners........ RCU has an excellent forum about batteries. It's monitored by at least one professional who is really, really good. It's a good place to learn about battery stuff.