Here is my take on your bike. You are indeed fortunate to have an original and hopefully unmolested machine with a known history. Its present condition is the result of the various stages of initial care, daily use and finally discarded as life's changes come along. A complete strip, and a better than new rebuild is all very well, but whether farmed out to specialists or DIY, the paint and polish costs mount up, and you will loose the essential time worn charm of a rare original survivor.
As it stands, my feeling is that for the time being you would be better off producing a reliable, running and useable bike, without the expense of a grand restoration to the finish. Clean off the flaky rust with a Scotchbrite pad and coat with water based satin finish clear varnish. This retains the existing patina, prevents further deterioration and is easily removed if you decide to go for a full cosmetic upgrade. Don't just rip it to bits, we have all done this, forgotten where parts go and damaged parts in a headlong rush to get it done.
Have a look for the paperwork, if the original documents are lost retaining the original number is straightforward, but may require an inspection of the machine by an authorised agent of the DVLA. They will want to see a complete machine, not a pile of parts..
Have a good look at the finer details on this very forum, you will find plenty to point you in the right direction. Anything that you don't understand, however daft it seems, just ask and save a sleepless night.
Welcome to the forum, keep us posted.
Swarfy.
