Re: Your 2nd question about whether you "should" update all charts, even those you have no intetion of using: That's simply personal preference.
It will take a lot of time to download all the charts that exist, especially the first time. (If you routinely update as soon as charts expire, you'll only deal with a subset of all charts for subsequent downloads, but you'll also be updating several times a year possibly for no useful purpose.)
Still, there's no harm in downloading all the charts. They're just data files, and they'll reside on the SD card, waiting to be accessed if needed. If not needed, they just sit there and don't bother anything. There's plenty of room on the SD card, so no worries about "overloading" the device.