It sounds to me like he needs more socialization and to learn to pay attention to you on walks. I know it feels like you can't keep his attention, but I have never met a dog whose attention truly can't be redirected. You can't just feed him or try to play with him. Try suddenly changing directions, zigzagging, running backwards, whatever. Keep doing it until he looks at you, then give him a food or toy reward for that. You might feel like an idiot but I promise you'll be able to get his attention.
When you see someone approaching while you're walking him, either start zigzagging, or if he'll do it, put him in a sit and ask him to focus on you. Try to do this before he starts staring them down. You'll have to pay a lot of attention to your surroundings. You may also have trouble keeping his focus no matter what when you're very close to other dogs, so if you find that's the case, try to keep a safe distance from them. Once he learns to ignore them and pay attention to you, you can start getting closer. Also, if he doesn't have one, teach him a "watch me" command--when you say it, he needs to look at you. You'll use that when you start to see his attention wander.
Just stuff to work on until you can get help. For what it's worth, he sounds almost exactly like my Hector was when I got him. Hector is now a model citizen--he walks on a loose lead even in close proximity to other dogs and people (even when said other dogs are barking and lunging at him!), greets new dogs politely, plays well, etc. He just needed to learn that new dogs and people aren't a big deal, and that I'm the one controlling things on our walks so he needs to not worry about it.
As far as the different types of aggression, this sounds like reactivity rather than true aggression. It doesn't really matter that much in the situations you're asking about though, because the response is the same for either--him learning to listen to you and let you take the lead on walks or in the car.
What kind of socialization have you done with him when it comes to other dogs?