Congrats!!! What a handsome horse. Ok, I am not an expert, I repeat, I am not an expert.
I have a 28 yr. Standardbred mare that I have had for 15 years. I also have an 8yr Quarter Horse gelding. I also work with friends to retrain off the track Standardbreds to pleasure horses. In my opinion you can never do too much ground work.
If they don't respect you on the ground, then they may not respect you under saddle. With that said, 1st off, if you have a nipper, don't hand feed. If you want to reward with treats, either put it in the feed dish, or on the ground. The nipping may take some time to get over. I have seen nippers that have come around, and can eventually be hand fed. There are some people that are just against hand feeding.
When you lead your horse make sure you are on it's left side, your right. You should be able to walk so that you are at an arms length away and parallel to his front shoulder. Never lead directly in front of him, if he spooked he could end up on top of you. If while walking you want to change direction, move towards your right so that he is on the "inside" of the circle. Keeping the lead rope in your left hand, you can put your right arm out straight while changing direction, this will help keep a safe distance. When you are walking in a straight line, (still on his left side)practice the whoa, and make him stand for a few seconds, then a "walk on". I do this every 3ft or so. Eventually, the minute I stop, my horse stops without using words.
As with our dogs, there are different approaches with everything, and it certainly depends on their personality.
Please feel free to email me trtwpsn@yahoo.com