Why would you want to spend money and have battery drain and be not able to do hardly anything with your console? There is a huge world you will be missing out on. If someone offered you free plane tickets to go wherever you wanted to, would you choose to spend money just travelling by bus?
This analogy (like the beef one) isn't exactly applicable. I'm perfectly happy leaving my 3DS as is, I bought it to play Metroid, and I've done that. It could sit in my closet and I'd be fine with it. I have some friends who play other games (like smash, animal cross, pokemon) that I'll play with them occasionally, and it would be nice to play some older games from time to time for nostalgia's sake. The $40 is meaningless to me, I make more than that in the time it would take me to flash the firmware.
That said, from the sounds of things, cfw has come a long way since my friend got his r4 (He heard all kinds of horror stories about cfw, but this was years ago). So I'm not opposed to give it a shot, especially since the DSTWO plus is out of stock and the $20 is available.
In regards to ROMs, is there a reputable source you can tell me about? I realize it might not be something anyone can post. I used to use a website to get most of mine, but they've since been hit with a lot of DMCA take downs and don't have much of a selection, let alone cia files.
Use freeShop - you can download and install right on your console. There are instructions on the OP of this thread to setting it up.
My last question is, how difficult is it to undo this process if I want to set it back to stock, or is that even possible?
It's possible, but not recommended. If you install any system title that requires cfw to run then your console might not boot or will start behaving strangely (when that system title won't run because CFW has been removed.) See https://3ds.guide/uninstall-cfw if you want to uninstall it