> First question is does Linux now have a driver for these dongles. 

Maybe:
http://en.community.dell.com/techcenter/os-applications/f/4613/t/20001903

> Can W10 dual boot with Linux? 
Yes!

> If W10 can dual boot and you are in Linux and you get a windows virus, etc., is there a chance when you go back to W10 that the virus can move from the Linux partition to the windows partition and infect windows? 

> 4th 
Is it safer to just let a laptop be entirely one OS or the dual boot pretty good for people that really don't go anywhere scary? 

Maybe... Windows doesn't understand Linux filesystems by default, but Linux does understand Windows. So it's theoretically possible to pick up a Linux virus that delivers a windows payload over to your windows files, but that sounds crazy unlikely unless you're operating a nuclear facility for enriching uranium.

Technically having only one OS is more secure, so if you simply want peace of mind for online banking, find a cheap laptop and put Ubunto on it. Don't waste brain power trying to get every little driver working. I've done something similar for cryptocurrency.

Dual booting is OK as well if you want to reuse the machine for other Windows things, even if it is theoretically a little less secure.

You could also experiment, test the waters, with a virtual machine using https://www.virtualbox.org/wiki/VirtualBox
This won't protect you against keyloggers, but it will soundly defeat run of the mill malware and viruses