In your world there will be no cart before the horse. you are best just getting as many parts as you can as 5700 parts are NOT dime a dozen. So yea you know you want fenders so put it out there. once you get it cleaned out.
On a nice sunshine day. Get a lawn chair a 6 pack of your favorite. then just sit there stare at it and let it speak to you as to what it wants to be. write it all down. if nothing comes to mind the beer speaking will help smile take a few laps around it.
then plan your build and start your search accordingly. Then tear it down and find out what is missing or is going to be a real pain in your build and decide the routes. Since you know you will need to source some items in the long run on something that may take a while it keeps you ahead of the game. Also in your situation not having the long term game plan may be costly. having to go back and forth on a few things. my rambling for the day is done. enjoy the ride.