With that amount of work and especially being a convertible you should have the car supported on a rack the entire time and weld in additional support braces to secure the immediate areas you are working on.

As previously stated you will need a "logical" plan of approach in selecting which areas to work on first using the original panels for reference points.

IMHO it won't be long into this project and you'll begin to think sending it out to a shop equipped to handle it was a real good idea.