From the sounds of it, this tower has possibly been abused or reutilized several times over the years. I'd be leary about putting it up as a free standing tower without some guying. If you are determined to have it be free standing without any sort of guying or bracing, be sure to go over every weld to ensure there are not cracks. Also check all of the members for breaks, bends, cracks or other deformations.
Your soil conditions are not great for putting in a good foundation. You will probably get some frost jacking of the foundation and it will be tough to pour concrete with the shallow water table. You may want to look at a precast "pile" or similar foundation system to get your foundation below the water table slightly.
It doesn't sound as if you will have too much issues with direct wind loading, but you will want the minimum amount of concrete recommended by the manufacturer to start out.
If you can bury a section of tower into the concrete base for your new foundation with plenty of reinforcement to tie everything together, you will loose some height, but it would be a stable foundation. Getting it to the site and installed could be an issue if it is a boggy area. Equipment likes to sink and I wouldn't want to try to get a concrete truck into a swampy area (drivers don't like getting their trucks stuck).
As to removing it from it's current location, get your hands on a gin pole and a tower jack, then start removing it one section at a time from the top down (IF you can safely climb it). If you are unsure about the climbing aspect, rent a zoom boom forklift with a basket. Have someone tied off in the basket will all appropriate safety gear, tie off to the tower above the middle with enough slack to rotate the tower, raise the tower section slightly, release the bottom, then continue lifting until clear. Once clear, rotate the tower and lay it down on the ground; then disassemble into the 10' sections.
Good luck on the project, it is a good price for the tower; be safe with it's disassembly, relocation and installation.