I’m pretty bad too Nick – macpuppy will tell you some tales !! – and part of the reason for getting one, and now another, old bike off a mate was so I could faff about making mistakes and it wasn’t the ‘real’ bike..
A list of things you might need to fix, and the tools (and spares) required would help as a start, just for your own peace of mind. I have an upper limit on what I reckon is reasonable to fix (which is low than many). Have built some wheels though.
For me the complexity of building (not repairing) a bike is getting the compatibility stuff – i.e. if I buy this brake, will it work with this lever and this hose/cable. Same for bottom brackets, MTB/road, for chain sets, for chains, shifters. No wonder I prefer SS 🙂
Chat up and LBS? go to a mate’s with a bike and some beer and dismantle / re-assemble.. take a bag of bits and replace…