Hi JR,
2.4GHz
Likely to have further range, although more interference with other 2.4GHz electronics, such as a cordless telephone. Speed is slower.
5GHz
Range likely to be less, speed is higher, and less interference with other electronic devices.
Having two - 5GHz modes
Do you mean having a guest account? Some routers allow you to add a guest mode, i.e.
2.4 GHz
2.4 GHz guest
And that allows someone to connect to your network without having access to your shared files or hard disk.
Some routers let you set up multiple SSID's. You can run several different WiFi networks at the same time and they all show up on your WiFi list when searching for networks from your computer or mobile.
Rebooted
Well, I think things need to be rebooted from time to time. Just like a car needs to be started once in awhile and not left sitting. I think the same principal.