As the others have said Moto Rapido will get many parts to you almost before you have ordered them
and eBay will become your friend if you are looking for 'period' modification parts but some are getting stupidly expensive.
As with any older motorcycle the main issues that cause problems are age related and in the twenty years I've owned my 900 it is the effects of Ethanol in modern fuel that causes problems, particularly the Vacuum fuel pump.
In addition, a lot of the wires were already of marginal cross section for the expected current- typical examples are the yellow wires from the alternator and the red ones going to the 30A 'Maxi' Charging Fuse under the fuel tank. Both of these are something like 14AWG (at best) whereas to be capable of carrying 30A they should be at least 10AWG, couple this with oxidisation in the crimps means they can get hot and begin to melt the insulation.
We look forward to seeing pictures...we like pictures here