The best way to start would be how to use it as intended: familiarize yourself with how to install and play steam games, rebind some controls, update it and so on. I've found quite a bit of 'tips and tricks on what do do when you get your steam deck' on YouTube, but the main one i use is the requested fps: instead of 60, 40 is better (battery wise) with a lowered... I forgot the name of the setting. In either way: it really helped on battery drainage.
Protondb.com is an interesting site in that it maintains a database on which games are(properly) playable. It's more reliable than valve's own rating system.
The deck is pretty much a pc with a nice front end. You don't hack it any more than a windows pc. Just press 'go to desktop mode' to go there. It runs Linux, but by now it has plenty of ways to use it with hardly needing windows skills.
For emulation, google "emudeck" (oh, and Google "hero launcher" as well if you have gog.com and/or an epic games account you want to use). It's almost down to one simple install interface to download, install and configure most if not all emulators for it. You have to provide the roms and a firmware here and there, but otherwise it's smooth sailing. It even grabs images to use as covers and puts the games in steam groups for you (meaning: you'll find your roms in gaming mode between your steam library).
You might also want to Google decky loader. It's... Kind of like the homebrew channel, but free. By itself it just provides an easy way to install plugins. But there are some fun ones there.
Installing non steam games... My method's a bit clunky, but perhaps the previous option offers a better way (not yet checked).
