1: I don't know about the dude in the LAN party video, but in my own experience I've been fussed at more than once for hanging things like a tablet from the seatback. It's purely arbitrary, I'm sure, but the FA rules and you have to do what they say. So hanging a monitor from the seatback may or may not be allowed, and it's purely up to the FA to make that determination.

2: I, too, would suggest just using a laptop with better battery life, simply for ease of use. I used a MacBook Air for many years, and now use a MacBook Pro. I am able to run VMs on it (ran VMs on both, actually, without issue) and have been able to power both using small power supplies if I needed to recharge (and the aircraft had seat power). The MBA could be powered from a 45W very small adapter, and my MBP can be powered by a 65 or 100W USB-C PD charger that is exceptionally small (GaN charger).

You gotta remember, you're not only carrrying a monitor, keyboard, and mini-PC and power supply on the plan, but you gotta schlep all that through however many airports, then to and from the hotel, and wherever else you gotta take it. IMO, the less crap I have to carry around the better.