I use Strawberry for mine.

Yo dawg, I heard you like emulating, so I put an emulator in your emulator so you can emulate while you emulate.

More or less. I think there are some differences between the Q and K based models, but they’re close enough to not require separate ports of Rockbox.

You should look into Rockbox. It’s an open source alternative firmware for a variety of portable media players that adds features such as support for more file formats (and it runs Doom). As for which supported players I’d recommend then maybe a flash modded iPod or an AIGO Eros Q or K (also sold as the HIFI WALKER H2, Surfans F20, or AGPTek H3).

Are you referring to a drawing tablet? If so, then a good number of ones from the better known brands are supported by the kernel by default. Your safest bet though is Wacom. Wacom is definitely the best supported brand, but it tends to be more expensive than other brands (such as XP-pen and Huion). Non-Wacom branded tablets may require a little bit more initial configuration, like adding a udev rule (I had to do that for my Huion Inspiroy Ink).

Qmmp can use them too.

The thing you’re looking for is called an Input Method Editor. The only one I’ve ever used on Linux is Fcitx which I really liked. I haven’t used it in a few years though.

This is the homepage for the current version.