I like to get the bike completely mechanically sound, running, and road worthy before I tear down for cosmetic work. That way you are much less inclidned to scab up the bike fixing mechanical when it's all nice and painted.
For me it's not about a 100 point concours resto. It's about either evaluating if it can be brought back to life with minimal repaint such as my recent commando. Kept the tank and side covers original even with a few blemishes and repainted frame and polished alloy.
Just polishing and keeping fresh like my K6. Just keeping it clean and running great, even with patina on the plating etc.
Keeping it completely original with all it's fine patina and blemishes but mechanically perfect like my Trophy, right down to everything except tires and air filters. And they are as original as can be.
A frame up job like my Dream including exhaust, paint, seat, and tires as close to the original white walls I could get.
Or mostly original with sensible updates like the Lemans, departure from stock would be all SS allen hardware, SS brake lines.
Then there is the K8, Not original really in any way but tastefully done so as to fully reflect the original bike, just happens to have a side car on it. Most people cant tell it from stock. Paint and pipes and seat are the only real departures. I didn't want to spend the bucks on pipes and worry about decals etc.
So you really need to understand exactly what you want to do, what you have, what it's worth, and what you are going to do with it. I ride all my bikes. I make sure I switch all brakes over to dot 5 to keep them maintenance free, make sure they have AGM batteries in them, I keep a special mix of fuel in them (premium gas, stabil, lead additive, and 70:1 two stroke oil mix) that keeps tanks from rusting and everything fresh. I always drain carbs if I'm not going to ride the bike again in 4 or more weeks, that way I don't have gummed up carbs, ever.
Soda blasting is your friend on cleaning parts without eating them up much. Good old duplicolor engine paint looks real good, close to original, is cheap, and goes on easy. I tend to use Acrylic Enamel with hardner to paint body parts. It's tough, easy to apply, cheap (I get it over the internet). I shoot all my own work, you can easily teach yourself (I did). Lots of info on body shop sites. Spray guns are cheap. My old CH gun must be 30 years old but still does the job and was only like $20 back then. Prep and clean air are the secrets. Sometimes I paint frames with a rattle can (Norton, K8) as that more closely matches the original (not too much gloss). Sometimes I just want a nice shiney bike so I shoot the whole thing with enamel (Dream, LeMans). Some good polishing wheels and compound are good to have as well. Most original bikes did not come with mirror finishes but a nice satin finish to the AL. That is easy to reproduce with a wheel. Some guys get carried away with polishing. Unless you clear it it won't last anyhow. And if you do clear it, you will end up stripping it and redoing it before long as clear just does not last. Didn't when the bikes were stock and has not improved any since it seems.
So what is your goal?