I don't know about some of this advice. Horses never give up their feet just because they trust you, they have to be trained to give up their feet. When you start working with his feet their is a great book out their from 4H that gives you the basic handling of a horse. It shows you with pics and easy to understand guidance on how to pick up a horses feet in a safe manner so that you don't get kicked.
All horses are born head shy, and unless someone told you that the owner was hitting him about the head, it is natural for horses to be head shy. I'm a human and don't want people putting their hands about or in my face.
There is nothing wrong with taking some time to get the horse used to you, but if you took a horse to a trainer who would be a complete stranger to the horse and be in a new surrounding the trainer would get down to business.
If you decide to do some desensitizing make sure that you don't release the pressure until the horse shows signs of relaxing licking their lips, standing still, lowering their head, cocking their back leg, not pinning their ears all signs that a horse is relaxing and accepting that they are going to be ok.
Not all resuce horses have been abused some have just been neglected. No one paid attention to them and they may have not had good food, or very little intereaction with humans. I would treat it just like it was a foal a blank slate and start off like you don't expect it to know anything, except for what you begin to teach it.
If it is feasible have a vet give it a good looking over. I would look for a farrier now because this is a busy time of the year and you will probably have to wait a month to get a appt.
Treats are nice, some say don't give by hand, some do. I give treats when there is a fence between us
some horses will mob you if they suspect you have a goodie on you
it kind of depends on your level of what you feel comfortable doing now as well as your future interactions with the horse. My sister loved treating the horses and although I warned her, one day she went in and the horses started chasing her looking for those treats lol it was hilarious, it was very muddy and she could hardly keep her footing and it scared the crap out of her. Needless to say she started treating only through a fence and not everytime.
You should do a lot of reading, talking to others and watch videos because the horse will only progress as you progress.