Welcome to the board.
Most of us would probably say get the most for the money. As you said you have limited knowledge on the subject. IMO I'd start by visiting your local tractor dealers as that is probably going to be your lifeline for repairs etc. There are many good stout machines out there but most would agree for a newcomer to tractors look at the major players such as Deere, Kubota, Massey, Mahindra, New Holand etc. Sit in seat on as many as you can. For 5 acres you'll probably find yourself in the ~30HP range. As far as impliments I would expect something to remove snow from the driveway, a chain harrow to drag the pastures, a rotary mower, a boxblade is indespensible as well as a front end loader. A lot will depend on what your area is like. I wouldn't worry to much about moving snow so the horses can move around as keeping fresh water unfrozen. Horses have are amazing at what they can and can't get around in. As far as expense on your tractor purchase you will most likely have some sticker shock and you should be prepared for it. As for buying used that is also an option but you'll find that prices don't depreciate much on tractors as you might think. With new you get the comfort of warranty. Hate to bring this up but unless you buy from a dealer or have a good neighbor to haul the tractor you'll be looking a a good stout trailer and possibly a truck. This is another reason to take your time in this endeaver. So many options.
Bottom line is a tractor is indespensable around multi-acre properties. Can you get by without? Probably but the amount of work that you can accomplish is amazing. Besides the sheer fun of running a tractor, moving mounds of dirt (or manure) can be very relaxing after a hard day at work.
Good luck on your journey into heavy machinery.
