You need to keep in mind that most laptops are not going to have 2 ethernet ports(or even 1 these days). You will need 1 port to connect to your modem and 1 port to provide the network to an AP. All ports aren’t created equal. If you want good speeds you want to find something with 2 good ethernet ports. Your internet speed will determine what is good enough for you port wise. If you are fine with pretty slow speeds then a laptop can work and you can use a usb to ethernet adapter but that’s a bit janky. If you intend to use the built in wifi card for the AP just know it won’t be nearly as good as a dedicated AP. Check out the Lenovo ThinkCentre line. It has some good options with decent ports. As for a UPS you can sometimes find something better by looking at “Solar Power Generators” instead. They’re basically just batteries with an inverter and outlets on them. And they can recharge from solar which is why they have the name. But a lot of times they’re the better bang for your buck than a normal UPS. And if you got a few solar panels you could hook them up to it. Which it sounds like might be useful to you in general.