I done one for a mate many years ago. Took me about 10 weeks to complete and that was with him doing all the running about to the powder coaters etc.

Search for 'Another rear end resto gold cup winner' and it may give you some ideas.
It can be done just be tidy and store parts away untill needed.

Also depends on car and condition usually doing a job like this opens a can of worms on anything.

In the process atm doing a M3 not a full underside but complete suspension with some rust issues to be resolved and its taken me a lot of time.

Good luck