Where do I start?

What is your intention? Refurbish? Rebuild? Convert to r/c ? Build one like it?

Looks like it already was set up for radio control Probably first thing is to fill the bathtub and see if floats, or lays on it’s side. This will tell you if if “can” sail and then a review of what electronics you have versus what you will need. There are guys on the site that are into vintage sailboat designs and if you post specific questions, they will jump in to help with ideas, thoughts, opinions and even “how-to-do-it” offerings.

The answer will depend on what you want/expect when done.