Why use a Delorian for a time traveling vehicle? It's stands out, is too futuristic looking, has doors that open differently from every other car, and it costs a lot; what if the vehicle gets damaged in the past? Why not just get a car that's easy to buy spare parts for.
Doc answered that in the movie himself.
"The way I see it, if you're gonna build a time machine into a car, why not do it with some style? " There was also something about its stainless steel construction playing a part in his decision, but I don't remember that part of the quote.
Why did McFly even have to find Doc in the past and then go about saving Doc from getting gunned down? All this could have been avoided by Doc simply setting the clock to go back one hour so Marty would appear an hour earlier and tell Doc he's going to get gunned down. This way the gunners can get arrested, and Doc will have two time traveling vehicles and current-timeline supplies to repair it with.
Again, something Doc answered in the movie himself. He didn't want to do anything to change time. Especially after seeing the consequences of what happened with Marty.
His plan was to have Marty reappear at the exact moment he left so nothing looked to have changed. Marty's the one who said "fuck it" and set the destination clock back early enough to try and save Doc -- his only problem is that he didn't give himself enough time. Plus he's a teenage kid. Not too bright to begin with.
Did you even watch the movie, man? XD