mu4e because it’s the best email client which runs in Emacs.

Q1: Pretty good! Use ProtonDB to check what games work, and if you need to apply any fixes.

Q2: Linux Mint is the most popular choice for beginners, and it’s extremely easy to use. Other people choose Pop!_OS because it’s apparently better for gaming (I haven’t tried it). However, I think the best distro for gaming, while still being extremely stable, is Nobara (a distro based on Fedora Linux).

Also, practically all Linux distros are customizable, don’t worry about which one’s the best.

P.S: You can browse through the most popular distros here: DistroWatch

(Background: I’ve been obsessively using Linux for four years.)

Don’t listen to this guy, use GNU Guix.