Full rebuild Commando 750 fastback

If it were me, I'd try to put it together first, doing the minimum to make it go, and ride it. Then you'll 1) know whether you have all the bits and 2) learn about the bike.

Everyone slags off the Haynes manual but I think it's pretty good and features your model.

the Norton manual by Norman White is widely thought to be very good. I have read it and recommend it as a first step, which will give a vg overview and specifics about all the stuff you will have to deal with.

Get it built back together, run it and evaluate the level of wear, any sound tank will do for this.  I rebuilt a mk2a a few years back and found it to be a very neat machine to strip and rebuild.  But if it ain't broke..... drive train that is tested and found to be  in good order will save you a huge chunk of time and money.  Enjoy it!

Electrics is the last thing to fully complete on any rebuild. All the electrical bits need to be in place before worrying about the loom/wiring, after all the coloured string just joins all the bits up. And you can't wire up bits that are not in place. But if you are going to run the bike for a while and you have points and the advance/retard is shot then the ignition will possible be all over the place. So you might just have to buy a new electronic ignition just to get it usable.
Battery charging is not crucial as you have at least 50 miles or up to 100 on a well charged battery. When/if you get to this point then a direct contact on your specifics ideas/problems is advised.

I would start with Norman White's excellent book.  I can also recommend a series of YouTube videos by an American contributor called " The Mighty Garage". He rebuilt a Mk2 Commando which I found very useful.

The hardest problem I found when I built mine back up from a box of bits was the Cable (electrical) routing. I couldn't find many pictures or diagrams of where the wires should run. 'Things' where disconnected and moved a number of time to find a tidy route.

I rewired my 1971 750 Fastback from scratch, so if you need I could send some photos showing where everything goes. I would recommend replacing the regulator/rectifier and Zener diode(s) with a Podtronic type unit. What year is it? Be aware that pre and post 1971 the wiring diagram and electrics change completely. Pre 1971 the wiring has similarities to the Dominators and is much simpler. Mine is on the cusp of change, it has the old wiring but some later parts, such as the centre stand, so is clearly an interim model, possibly built in 1970 and sold in 1971.

The Haynes manual will allow you to do most things, but I also have the Norton Villiers Commando manual which has detail in it that amplifies information in the Haynes. I use it all the time, mine is very dog-eared. I think you can still get it from Andover Norton.

There is nothing wrong with Zener diodes, they have been going for over 50 yrs. But it would be wise to check the actual voltage of them (I can do this) also the original Lucas plate rectifier some times shows its age with bent fins and corroded terminals, replace with encapsulated square version (I sell). Reg/Rect if all else fails.

They are simple, especially relative to modern vehicles. However, that all depends on the owner's background and understanding, as is often shown by the questions that come up.....
   A lot of problems occur when old (50 plus years!) wiring harnesses are used: corroded connectors, insulation worn through etc etc, particularly the mass of connectors under the middle of the petrol tank , which get even more neglected than the others!
   Grant Tiller has done some good wiring diagrams, in colour, which are easier to read. Plenty of reading and digesting info will be worthwhile use of time at this stage, as I have done over 40 years of involvement...!

The three featuring the late, great Mick Hemmings are essential, covering, in turn: engine, gearbox, forks and wheels.

It's also worth getting the John Hudson versions, partly because of his years of service to Norton owners, but also because he does cover a few points that Mick does not.