Linux

No problem! About the USB drive, running it in a VM would not tell you anything about how it will run on the Macbook itself. I would recommend booting into the usb in a 'live environment'. Essentially, you boot into the linux operating system off of the usb and are able to play around and use it in a non-persistent environment. You simply plug in the usb and select it as your boot device. If you decide you like it and it works well, installing should be as easy and following the steps in the installer. The reason running a VM wouldn't tell you anything is that VMs are virtualizated, meaning they don't directly run off of your computers hardware. The drivers used for virtual machines are their own unique virtualization drivers, so for these reasons running linux VMs is separate from linux compatibility on bare metal.

Here is an explanation of those questions:

2. This is less important when choosing your first distro, but some users have varying preferences on package managers. The package manager is responsible for installing and updating everything on your system (everything; applications, libraries, and the kernel) that has been installed via the package manager. Some package managers are distro-agnostic and are installed alongside your distro's package manager, like Nix or Guix, although you don't really have to worry about these. The package manager is baked into the distro you used and cannot be changed, and some distros have the same package manager. For an example of a preference, dnf (Fedora's package manager) commands are much more verbose than pacman (Arch's package manager) commands.

To show what I mean, here's the command for installing a package with each:

dnf install

pacman -S

Some find the letter arguments of pacman more confusing.

An example of a preference I've observed is that I prefer dnf's search results over apt's (Debian's package manager), although apt search is much faster than dnf's. Little things like these don't make a huge difference, but the package manager is something you will interact with a lot, so watching a quick video or guide on a distro's package manager can't hurt.

4. A display server is responsible for displaying your graphical environment. If you have your laptop open and you're looking at a few windows, the display server is responsible for the placement, size, and content of the windows. Everything graphic on a linux system is handled by the display server. You have chosen to get into linux in the middle of a sort of transition period from the older X11 display server to the newer Wayland display server. Wayland is newer, more secure, and overall snappier / less screen-tear-ey. X11 is older and not receiving development, but is tried and tested, much better for accessibility needs than Wayland, and more "self-contained" (i.e X11 is not just one program, it contains many programs to make interacting with the graphic environment easy and consistent. Wayland leaves these integrations in the hand of each "compositor")

Desktop environments and window managers will either:

1. Support Wayland and X11
2. Support only X11 (Many X11 only examples have forks that support Wayland)
3. Support only Wayland

As for your applications, some may or may not support running on Wayland natively, which is a non-issue as the program XWayland will automatically run X11 only programs through X11 on your Wayland desktop.

TL;DR on the display server section here: One day you will have to use Wayland, but today is not that day. If Wayland covers all the functionality you need, and you do not use NVIDIA (Wayland on NVIDIA is not in a good state currently), I would go with that. If accessibility or easy software compatibility is your aim, go X11.

5. This one is easy, let's say you've decided you 100% want to use the Cinnamon desktop environment. Linux Mint has three spins (All that 'spin' means is a version of the distro with that desktop environment pre-installed): Cinnamon, MATE, and XFCE, however not all distros offer a Cinnamon spin. If you wanted to use a distro that does not offer a spin of the desktop environment you'd like, download the 'minimal' iso for that distro. Some distros call this iso a different name or might only offer a 'server' iso that fulfills the same purpose, but basically you'll boot into a tty (terminal prompt) and you can simply install the desktop environment you want via the package manager.

I hope this helps and isn't confusing!