Thank you so much for the detailed reply. I had not even considered a PA system, but that would be super helpful if his guitar playing friend comes over as well. We do have a Katana 50 MKII amp for another kiddo (they hate each other), so not bandmates. I'm going to have to do some research on this equipment to see what lines up used, but on a cursory glance, this generic equipment seems to be plentiful on facebook marketplace.
Are you talking about these? https://www.amazon.com/dp/B079PTW3K5/ That's one item that I was thinking about.
Thanks so much for the counter-opinion on the EAD10. It does look like I can get a decent budget two-mic setup used vs trying to find a below market EAD10. It's definitely a few more wires.
Earplugs have been a huge problem, my dude has some really weird shaped ears. I've tried several different brands from Amazon and none seem to make a great seal. I was thinking about these Vic Firth headphones: https://www.amazon.com/dp/B079PTW3K5/
Right now he's got the regular ear muffs on.