Thomas, when I was looking to buy a tractor at the end of last year I was wanting to buy a 4700 4wd. My decision was between a 4310 hst (because it is so easy to operate) and a 4700 because it was bigger, stronger, and more powerful. I chose the M series because I would be clearing a lot of land. It sounds like you will be clearing land, but it also sounds like you will be using it to help you build. Need to let us know how you intend to use your future tractor.
Wen has a great suggestion. Instead up buying one tractor, using it, going through the hassle of selling it, and then buying another tractor, why not just buy the tractor you want from the start and be done with it.
One of the ideas I had when I was buying was to buy a beat up 4x4 60 hp tractor at a good price, doing all the hard clearing work that need to be done, and then selling it, and buying a new tractor that I hadn't dogged out. After looking at prices of used tractors and realizing they weren't that great of a deal, I decided to just buy what I was going to use over the next several years. I have been happy with that decision.
One other thing to remember, you are buying a tractor not a tracked frontend loader or a bull dozer. When I first started working on my property I was trying to get my tractor to do jobs it just wasn't meant to do. I finally hired a grader who used a CAT 931 (tracked loader) with a 4-in-1 bucket. What he did in a week I couldn't have done in a year. He charged me $2,650 which has been the best money I've spent on our ranch thus far. He charged $55/hr.
So my suggestion is to buy the tractor you think you will use over the next few years, and to hire someone with a CAT to do the big work.
Now to your questions...finally.
1) When buying something used, offer low...a lot lower than you expect it to be. That is a good starting point. When I was trying to buy a tractor this past Fall, I found a 1998 4700 4wd, with a canopy, but without a loader, and with 16 hours on it for $17,900. I offered $16,000 and the dealer didn't budge. I offered $16,900 and told him that was as high as I'd go. He wouldn't come down in price at all. I walked and found a better deal about 2 weeks later. About a week after I'd bought my tractor the dealer with the 4700 called me and was willing to take $17,300. So I'd say the 4700 your are looking at should be less than $17,300 (It's a year older and has more hours). Call a dealer and find out what a new loader costs (I've forgotten) and take off 10% to 15%. Then take $2000 off your total and that gives you your beginning offer...and who knows, maybe the man says yes to the deal.
2) Tractor should be easy to resale but will take a little time. If you plan to resell make sure it is well maintained and very clean. Advertise it in the Equipment Trader magazine.
3) I think it would be more stable, but be really careful of any slope that's "not so gentle".
4) Wen is right, a 48" tiller is really too small, especially for a 4700. To rework my place I've been using a box scrape, all purpose plow, and front end loader with teeth.
5) I haven't bought forks yet for mine so I don't know the cost, but I did get a quick release, heavy duty bucket because I will get the forks after I build my barn. Does the 4700 you are looking at have a quick release bucket?
6) You may want to look at a 3710 hst. This may be more tractor than you need, but the cost new will be about what you will buy the 4700 for. After you are done building, how do you plan on using your tractor?