You're absolutely right about Linux Mint. You can think of it like a curated Ubuntu. I'd recommend going with the Cinnamon UI. I've been using this combination for a few years now. About once or twice a year, I fire up a few other distros on one of my spare laptops at the house just to see where they're at. Mint is just a step ahead of the rest.

For your "mini-command-line" utility, I'd recommend picking up Guake terminal, and using the very easy hotkey mapper to map opening the terminal to something dead easy, like LeftAlt+Space. Guake is totally configurable, but with those simple hotkeys, you'll get a terminal. When you're ready to switch back, hit the hotkeys again and it will hide the terminal (keeping your session live). It supports multiple terminal tabs, which you can also switch between with a configurable hotkey (I use Ctrl+Shift+o and Ctrl+Shift+p to move left and right, respectively). Of course the display is ultimately configurable, too, so you can have it docked basically anywhere, transparent if you'd like, or as big or as small as you'd like. Highly recommended.