I'm not a pro but I've been filming for about 3 years now. It's not really an easy question to answer to be honest. Depends on the set up and where the deer might come from. If you know they are only going to come from in front of you then you can actually put the camera guy at the same height as you but most of the time you'll want them a little higher. It also depends on if you are in the same tree or not. If you are in side by side tree's then you should go around 3 to 4 feet above for the camera guy. If in the same tree then you'll need to look at shot angles and such. If the deer comes from the camera side you'll need clearance for a shot so 4 to 6 feet but probably closer to 6 feet so you can shoot under their stand if you need to. If in the same tree then I like being 6 feet higher and on the side of the tree. Sometimes on bigger tree's being on the back side is a bad idea. So being on the side of the tree usually gets you all the shots you need.
As far as a camera arm then that will depend on if you are self filming or not. If self filming then I set the arm about shoulder height if I'm sitting down. This makes it comfortable for me while sitting but still gets it high enough for me to use while standing. Just remember you might have to make adjustments in the camera after you stand up to shoot.
If you have a camera man and he is using an arm then he should have that arm about chest high so he can comfortably move it without moving any other part of his body. I do know that some guys will use a should mount for more freedom. I've not tried this and actually still think a arm is the best way to go.
On either one movement is the key. You want to have everything set up so that you do as little movement as possible. If you are having to fumble around the deer will see you as sure as the sun is up.
There will be mistakes and missed shots as that's all part of learning and you'll kick yourself for dumb errors. We've all done it. Just like in archery shooting, there is no substitute for practice and experience. Those are the two biggest things you can do to make for better film. And as far as an arm I'd get the best one you can afford. Muddy makes an affordable arm that will work on about any camera most of us can afford. It's probably the best one for the least weight you can get. Also give yourself some extra time. You might need 15 extra minutes to get everything set up and ready to go. Plus there are two of you now with double the noise and scent. If I'm on camera I prefer to be in stand 20 to 30 minutes earlier so that I can hook everything up and do a few test before it's deer time. Once it's first light you need to be up and running and ready to go.
I hope this helps