1) It really depends what hat you're going to wear, and if you're not a realtor it may be tough. The best way could be a friend trying to help.
2) If you have a license, give him your best estimate of what it could really be sold for and let him know you could list it for him. If you're an investor, you could make him a cash offer, but if he's not in distress/highly motivated, it sounds like something to go on the market.
3) You could try to get him a rockstar realtor and try to get some type of a referral fee. In regards to contractors, if there's no serious damage that needs repairing, estimate are not that hard to make on your own. If he's set on fixing and getting a better price, you could meet a few and vet them out to see who is best.
4) Step one identify how you can help him. Ask him if he'd rather sell as-is instead of spending money to rehab and definely have to list on the market after that. If he is not so much in need to sell quickly as you said but get his price, let him know what the price will be after fixing, and be sure to mention that no matter how much he puts in, the resale will be tied to whats going on into the market, not what he's spent, mortgage included.
5) Its fine to get involved as long as you know the best way to approach him and how you can be involved while still helping him reach his best interest. But as a side note, a lot of homeowners are unaware of true market value so the best you could do for him is get him the true value of his home. Even if its less than what he expects, you're giving him facts, and there's nothing more valuable that that.
Wish you the best of luck! And if he decides to fix it up, that will take time, so why not hurry and get your license so you can list it for him when its ready!