How dense are the trees that need removed? You said a bunch of 3"-6" trees is all yoou want out right now right?
The guy you got a quote from.....while $100/hr seems fair.....what is he using that is gonna take 10-12 hours per acre for? To me.....THAT seems out of line for just clearing and piling.
And 3-6" trees are pretty small. They would be no match for that 2wd 410 (unless you get into some mud). Should be able to push anything 6" diameter down with just the front loader.
And a grapple for either of the tractors would be real handy, so look into that if you do yourself.
Depends on how tall and thick the rest of the brush is, I'd probably attempt to bushhog everything first, going around all the trees. Once opened up, you can see what you need to remove, then start at it with the backhoe. And alot of the smaller brush that is too big to go over with the bushhog, can be pushed out even with the smaller tractor and FEL and piled up to be burnt.