Unless your goal is a show bike I don't see any point in rebuilding something that might not even need rebuilding.
Get on the road by:
1. cleaning the carbs and replacing all carb gaskets (leave the brass alone, the jets in most carb kits suck),
2. replace all fuel lines and clean the screen on the petcock that is inside the tank (you get to it by removing the petcock),
3. lube the cables,
4. do what you need to to get the front brake working, which might be as simple as bleeding or as complicated as rebuilding the caliper and master cylinder. When I bought my '77 550k it had been sitting in storage for over 20 years with 7,700 miles on it. It was 100% original right down to the tires. All I did to the front brake was pull the pads and piston and clean them up, add new fluid and bleed. I didn't replace the pads or lines and it worked just fine.
5. Replace the tires, tubes, and rim strips,
6. Do the 3,000 mile service from the repair/owner's manual
7. wash, wax, and ride.
With my bike it took a few weekends of work, but when I was done I put on over 4,000 miles in 3 months with no issues at all.