Cathy, As far as deciding how far apart to space the rows in the garden, I've just tried experimenting with different spacing. When I had the 17" walk behind tiller, I set out my onions in rows that were only 26" apart and other things 3 to 4 feet apart, but when I got the 40" wide tractor and 40" tiller for it, I spaced the rows 60" apart and could drive between the rows with the little tractor and tiller. Then when I got the B2710 with R1 (ag) tires and my rear tire width is about 54", I spaced the rows closer together this year (actually 47" just because I had a piece of rebar that length handy to use in spacing - very scientific/w3tcompact/icons/wink.gif). Then I used a 6 tine cultivator plow (about $150) on the 3-point and I drive straddling the rows with 3 tines on either side of the row. And yep, if you get careless in your steering . . ., well, I only plowed up about 10' of turnips and a couple of broccoli plants/w3tcompact/icons/frown.gif. The only other problem with that method is the fact that you can only do that until the plants get to be 12" to 18" high so they pass safely under the tractor. Since the garden's produced more than we could use and give away (I even gave some and sold some to a fruit and vegetable stand operator), next year I'm going to make the spacing about 72" so I can easily drive the B2710 and tiller between the rows. Your best bet is to buy a tiller that's the same or slightly greater width than the tractor, but finish mowers and tillers are both expensive. Brush hogs are much cheaper for pasture mowing, but it can certainly be done with the finish mower if you only have grass and weeds; no brush or rocks.
Rust on the disks doesn't hurt anything; using it will let the dirt remove the rust. Where rust hurts is the bearings. If they are not damaged, you may only need to grease them. If they are damaged, they simply have to be replaced.
Using a moldboard or turning plow, followed by the disk, is a cheaper alternative to a tiller for preparing a garden for planting; may not be quite as smooth as a tiller does, but the majority of the big farms in this area (corn, cotton, milo, grain sorghum, etc.) use only a disk prior to planting, but of course, they are using monstrous sized, heavy disks.
Good luck with your shopping, and you're looking at the right tractors, but go by and look at some blue ones, too, so JimBinMI can quit worrying about it./w3tcompact/icons/laugh.gif
Bird