I've had the same problem with my 4 month old colt. I imprinted him and he is playful and fearless. He is my first foal, so maybe I wasn't as strict early on like I should have been.
So anyway, after much frustration and a few tears, and several lessons with a good friend who has raised many foals, I now have him respecting me and moving out of my space (for the most part, not saying we are perfect).
What he would do is bite when I picked up his front feet or touched his chest (like yours does) and also bites and rears when being ponied. Basically, for my guy it is a playful behavior, as this is how he plays with my older gelding. But still, I can't have him playing with me, or the gelding when he is being ponied. So I bought me a dressage whip and carry it whenever I lead him and smack him good if he bites or rears. Same thing with ponying- if he bites or rears he gets smacked.
It has made A WORLD of difference! I also have been practicing just walking him and leading him a lot, and demanding respect and making him back out of my space (a lot). At first I was afraid to hit him, so I wasn't making an impression, and my friend pointed out that if he turns around and does it again right after I correct him, obviously the correction wasn't enough. So I got firmer and have a much improved colt!
As for chewing, biting my clothes, etc., I tried flicking him with my fingers and that didn't do much, so I smacked his muzzle a handful of times and now I can just give him a verbal warning and he respects that.
I would cry the first couple of weeks I got "tough" because I didn't want to be mean to him, but he HAS to respect you, or you will have a big problem on your hands when he grows up. So give tough love a try.
Another thing that helps my colt a lot is exercise. He is much better behaved after a good run than when he is fresh. Sometimes he is so mischievous that I can tell by looking at him he isn't going to behave well. So I turn him out to a bigger area to run and play (usually while I ride his mom) and when we get done he is a much better behaved colt.
I can't wait to get mine gelded too!
PS. I wouldn't avoid handling him in his stall/stable area. He should respect you everywhere you are, not just in certain places. I even handle mine while he is eating. I got the pinned ears/dirty looks a few times while he was eating and I was grooming him, and I yelled at him and shoosed him away from his food. Claimed the feeder as mine for a few moments, and let him come back. Basically you want to be the dominant horse, not him. That is YOUR stall, YOUR hay, etc, and he is only allowed there because you are gracious enough to share.
Last edited by trailhorserider; 11-10-2010 at 10:30 PM.