I agree 500% with scoutrider (and everyone else on here...). That's basically what I'm trying to say, in case my complete lack of communication skills confuses you, lol. Anyway.
Do you know anything about his past? That will help.
I'm sure there are people on here with much better advice and more experience than me, but I have had some experience with these kinds of horses, and it's pretty tough. I'm a pretty soft person with horses, so I have to keep in mind that sometimes, you have to give up love to gain respect- you may have to be harder on him. The trainer that was trying to lounge him was going a bit too far, hitting him hard enough to leave marks, but don't be afraid of being tough. Just remember: you have to find middle ground. Firm enough to get the message across, but not harmful. Smacking him with the end of the lead rope in the chest when he's crowding you won't harm him. If a horse can get kicked straight on by another horse and be okay, there's not much a human them self can do to them. Like has been said, it's about how you're using the whip that counts.
Is he with other horses? Watch him with other horses if you can- its always good to watch horses interact. It will not only give you necessary knowledge about how horses interact, but if you're watching him, how HE interacts, its even better- it will give you a LOT of insight.
Also, remember to always stay calm, patient, and be diligent- whenever I work with a difficult horse, I breathe slow and deep, and get rid of all emotions, and if I can't, I stop what I'm doing until I can, unless in a rare occasion when stopping isn't possible, although that's not often. And even if it takes half a day longer, I never stop on a bad note. That's important. Even if it's a tiny give from the horse, it's something. Like the trainer, who was hitting him- I'm assuming (correct me if I'm wrong!) that after a while of not getting anything, he just stopped. This tells the horse that even if he's getting hit, if he just doesn't give up, you will, and he'll get what he wants.
One more question to ask yourself/ keep in mind when working with him- what do you do when he does these things? That's a key component. For instance, if he's pushing into you when you try to lounge him and you even subtly back away or give in, he's going to notice. Even if you're smacking him with a whip, like that trainer, he's going to see that. Your body language is very important.
Hope this helps... I'm no trainer, this is just what I would do, judging from what I've read about him. I do agree that above all, though, your number one priority right now if you plan on keeping him is to find a trainer to work with both of you guys. Good luck!