Where to start with a rescue?

I have finally gotten my barn and pastures up to par for the horse that I rescued a couple of months ago, and he's home now.

He's about 4 years old, textbook quarter horse (though a little thin, skinny neck). He had a couple of minor knee injuries, and was broke to ride on a ranch in Oklahoma. He tacks up fine, and will let you put weight on him with no problems.

But... I have no idea where to start with this guy. He's a sweetheart, follows people around like a puppy, but I don't know what he knows or doesn't know.

Any ideas where I should start with training this guy? I'm probably going to just start at the basics.

Start with the basics. Try some lunging, ground driving, etc. If you're okay to get in the saddle, start as if he doens't know anything, ask him to walk on, then do some one-rein stops, and go from there. Does he know how to bend? Does he know what each rein means? Does he neck-rein?
There are so many things for you to do, it's really a matter of exploring.

I agree. What is his past?

I wouldn't be in such a hurry to ride right away. I would do at least of couple of weeks of strictly groundwork. Almost anything you do from the saddle can be done from the ground first including flexing and getting control of his hindquarters and shoulders. Plus, you'll be gaining his respect and he'll be more willing to please you. Just my opinion.

Not sure 100% of his past, and I am hesitant to believe what I was told of his training considering the source.

I was told he had 30 days under saddle, was broke to ride, etc. I can get on him and he will walk on a lead no problems. As soon as the person tries to walk away, he follows. I haven't tried to get on him without another person present. Maybe I should try?

I'm thinking I'll start with lunging and working on ground manners, at the very least to build our relationship. I would like to ride him soon, but I don't want to push it. He's eager to learn, so I don't think we'll have many issues.