My router has a pretty descent firewall so i feel like it should be safe? Maybe. Obviously I won’t be signing into any online accounts or anything like that on the XP machine. Is this a bad ideas? Obviously using Windows in general is a bad idea but I’m sort of limited by the hardware here.
I would avoid giving it internet access. You could probably get away with network access, but id still mainly restrict it to a disconnected network and just download anything you need for it from a modern machine. (Probably a shared nas for transfer.) If you’ve got a good router (ie not a isp or home router) you could give it access to specific items on a whitelisting basis.