I have recently started putting an NDA in our proposals. We just were sent another contractors proposal by an HOA for a project we are bidding on. I called the contractor out of respect and let them know they were doing this
The cool thing about general contracting is it is the same systems & processes to do big jobs as small just more digits on the numbers. If you can get dialed in on small projects it is very scalable
The first few jobs will be sort of a guess but if you audit every dollar spent and make sure it is assigned somewhere in your estimating system it is only a matter of repetitions until dialed in