The best way to get him used to a lead is to put his collar and lead on and then let him wander around the house with it on. You need to supervise so he doesn’t catch himself on anything. Border Collies are really intelligent so it shouldn’t take long. Once he feels somewhat comfortable you should try holding the lead and as you start walking coax him along with a small treat. Keep encouraging him with treats as you walk and he should quickly get the hang of it.
If he was never in a vehicle before it probably frightened him and a lot of dogs lose control of their bowels in that circumstance. So he may never have another accident. But you can try just getting in the van and sitting with him for short periods of time. Again give him treats and praise him a lot. When you think he’s losing his nervousness you might try just a very short drive and see how he does. Dogs learn rather quickly when you drive them to places they like such as a park, and most will soon look forward to going for a ride.
It was really nice of you to rescue him from his other life.