It seems that none of us know what your plans are for this guy. For all we know you got him to breed him, and every single one of us (including me) says GELD HIM! So what are your hopes for this guy? If you're looking for a quiet trail horse, you've got a long journey ahead of you, and that may never turn into exactly what you wanted.
I may be wrong, but based on your responses I'm wondering how much experience you've had with owning horses. While a trainer would be absolutely necessary, he can only giving you a starting point. You have to be able to replicate his success. Clearly this horse considers himself boss, until proven otherwise with everyone he meets (I'm assuming your uncle did not have these issues). If you don't think that you could do that in a safe matter, DEFINITELY consider alternative options. Being gelded this late in the game, he will most likely keep MANY stallion tendencies, and yes, may still be the dangerous horse he is now.
Finally, why did your Uncle give this horse up? He may not be very happy with getting a gelding back if he gave you a stallion so if you're toying with the idea of sending him back, be sure to discuss that with your uncle. If you don't think that your uncle wants him back, and you don't feel comfortable continuing with him, then list him for sale as a stallion that you can geld before sale, it opens him up to a whole new market. E honest about his behavior and need for an experienced handler and trainer. There are a lot of people with stallion experience, and a lot of those people may be better equipt to deal with his attitude. (which, I repeat, may not change a whole lot after he's been gelded- yes the hormones that rule his intentions will no longer be there in such force, but he's had 15 years to learn how to be an a$$ hole and will definitely need training.)
If your trainer refuses to come out until its warmer, get a different trainer. You don't need someone in a few months, you need someone now. And you're going to need someone willing to put in the time and energy no matter the temperature or weather.
Until you make a decision, I agree that spending time in his general vicinity will help get him acclimated to you and may help with his aversion to any contact with you. Just keep a safe distance until you feel comfortable that his isn't giving those aggressive signs.
Good luck and stay safe!