You'll definitely have to swap the bearings out, but they're not too difficult to do. Just need to find the right size socket to send them back in with.
If you're not desperate for them tomorrow, have a look at autodoc, (use the app, it's cheaper) you can usually get really good quality ones very cheap, but you do have to wait a couple of weeks for delivery.
Unfortunately, you'll need a 4x100 spacer for your RAs, the Porsche one won't be any good as it's an adaptor specifically for the conversion. Without seeing your adaptors, I'd say you probably need a large Alan Key or similar. Depending on the condition of the new wheels, I'd probably just take them to a tyre fitter and ask them to swap the wheels/adaptors over for you. Even if they charge you, it'll be cheaper than buying the tool.
Hi, I'm not 100% sure on what is happening, but have you heard of A2 Resource? Excellent site... https://www.a2resource.com/electrical/CE2.html Hopefully, that should take you though what you need to know.
As for things to look for, rust is the big one nowadays! Check sills, under the wheel arches (especially at the back) and behind/below the rear bumper.
I think there is actually a what to look for thread somewhere on here. Might be worth having a look around site and see what comes up.
