Appreciate all the feedback folks!
@ two_bit_score: Thanks for the welcome, and you were right, I got some good feed back and other ideas. I actually never thought I'd come back to Marion, but life has a funny way of working out sometimes. I used to train here (riding bikes and running) and it's crazy to see how much the area has grown up. 15 or so years in Houston makes one appreciate the country life even more
@txdon, bcp, Ed of all trades, ustmd: Appreciate the feedback. What I was looking at was definitely a root plow and not a ROOT PLOW.

Bill's Tractor supply in San Antonio carries a model close to it on their site for about $1K. I'm sure it's a good tool, and after reading some of the comments and my own research, think it's not right for me. I am seeing a pattern to outsource the job because I don't have the right tool for it, which is cool, it happens like that sometimes. I also don't want to have buyer's remorse and get a tool that isn't going to do the job or bust my tractor up and frustrate me.
@rlgustafson, jeff9366, tacboss: Thanks for the references and tips. I had been reading a lot about handling mesquite, and it seems to be a beast all of it's own. I want to stop it from taking root and think I'm catching it at the right time. Time, patience, and planning is what it looks like it's going to be.
*Update* With the ground being moist, I took a chance and was able to knock down and haul off, root and all, 2 of them and a bunch of saplings with the tractor. One more got pulled out of the ground with a chain and truck after I dug around it. That was enough for me; no stranger to hard work, but there comes a time of diminishing returns. Plus I had to get hauled out of the mud by my dad who is not letting me live this down. If he had facebook, me stuck in the mud would be on it! I think my next steps will be to get one of the local companies to come out and give an estimate on getting some of the bigger trees out. I'm okay with that because I think it'll pay dividends in the long run. Gives me more time to concentrate on some of the other projects I have for the property.