I think that is 20MB on the fly.
The PB will only use power to do the blinking light when it has is lid shut. It doesn't use the much power. My iBook sat over night, from 5:40 last night till 7:30 this morning, with the lid closed and it only lost about 3% of its charge. I even took it on a 2 day weekend without using it and it barely lost a charge. Booting up the computer is what takes the most energy, but starting from sleep, it takes less time to get to the OS, so less power to get back to a running state where you can start working again.
Probably the two things I can say about maintenance is Repair Permissions after doing any installation that asks for your Admin password. Found here:
https://forums.macrumors.com/threads/89736/
And MacJanitor to run Unix Cron jobs. Yes, OS X is Unix and uses some of the tools that Unix uses to keep itself in tip top shape. If you leave your mac on over night then these will run automatically, but if you want to do it yourself, then MacJanitor can make the process very easy.
Also,
www.versiontracker.com is a great place to find out about software. Type in a description of what you want the software to do, and it will show you the programs that do it.