i would buy used tractor individually. and then buy bush hog and blade separately. granted if they are selling them as a package or possibly from same person that is all good and fine. but it is fairly easy to find used bush hogs and rear blades easily on craigslist.
as far as buying used. i could really care less about brands, or model. but actually going out and physically looking at them, and test driving them. and checking hydraulics, and for leaks, and upkeep on them. a good clean tractor does not always mean it is a good running tractor. and a rust bucket of a tractor that has grease and mud all over the place, may be the best tractor out of the bunch. start the tractor up, test drive it, let it run for 30 minutes or so, so thermostate for radiator opens up. and engine warms up good. (may need to be in med to high idle for engine and things to warm up good) raise hyd 3pt hitch, and if FEL (front end loader on it raise it as well) shut off tractor and let it set there for 30 minutes or so and see if things lower.
test each gear of the transmission forward and backwards. check the fluid levels, (hyd, engine oil, antifreeze/water, secondary or third hyd oil location perhaps rear end, perhaps transmission perhaps up on front of tractor)
gas tractors are good diesel tractors are good. though if you plan on not running tractor and letting it set 6 months of the year. you may want to think about adding some sort of additive to the fuel. more so gas. so the gas does not go bad. or diesel does not gel up in winter.
you might try tractorhouse
www.tractorhouse.com lets ya search via zip code, distant, cost, and variety of other features.
hint: bush hog is an actual brand, what you are wanting is a rotatory cutter.