Be glad you aren't on Arch. Steam on 64-bit Arch is nearly impossible to set up. I also remember having to fight with Windows to get the dual boot going, and that was six hours of my eight-hour install. To be fair, getting Arch configured took days and days of nonstop work, but that's because I'm a perfectionist and I had access to Arch. These things do not end well. 
As far as getting acquainted with Linux, I would advise to just read up on everything you can. If you're on Mint, then the bulk of tutorials and instructional articles are written for Debian-based platforms like Mint, so you'll have a (theoretically) easier time. Reading about everything is one of the best ways to go.
Also, StackExchange is your best friend.
Steam on Linux is a mess in general, but with Arch being a distro without official support it's especially painful, yes. :r
OT:
On windows, I've used Wallpaper Master for several years. I have it monitoring two folders, one for each monitor. Very effective. I'm hoping there's some equivalent.
I'm pretty sure that the KDE Plasma 5 desktop lets you set up separate wallpapers (and a bunch of other things) through its activities, but my experience with Plasma is fairly short and rough, however I do appreciate it for the absolute plethora of customizability options, even though I'm a Gnome guy myself which within Linux is about as un-customizable as it gets, short of using Ubuntu's Unity (which is still a fair lot given the existence of plugins and all that).
If you do not want to change desktop enviroments (which is totally fine) one way to get that to work is to stitch two wallpapers together in your image manipulation program of choice with one wallpaper on the left, one on the other and setting the 'big picture' as a wallpaper in 'span' mode. I have no experience with Cinnamon or that level of wallpaper management though but that appears to be the only solution for Cinnamon specifically, other DEs like KDE or Xfce provide less 'cheaty' methods from what I'm reading.