About 4 acres of it are in Horse pasture, main task there is putting in gravel on the muddy spots, the horses do the rest.
Congrats on the purchase, I'm sure you'll be happier with a bit bigger tractor in the end.
With regards to the horses mowing parts, they'll eat the yummy things, but leave all sorts of weeds and brush that will need mowed to keep the grass healthy (or at least mine do). My dry lots get too bumpy to use a ztr or lawnmower, so I use a bush hog (rotary cutter). General rule of thumb on rotary cutter is having at least 5 pto horsepower per ft of rotary cutter (ex. 4ft rotary cutter should be used with a 20 pto hp tractor or larger). I fence off my "lawn" and graze my horses in the lawn during daily turnout much of the year 'cause why run the mower when the ponies would like to eat it anyway. Might as well only mow the stuff they don't wanna eat.
I've found renting a legit backhoe or excavator is the way to go in my case. The three point mounted backhoes just aren't beefy enough to dig a 10 ft hole. I can usually get a horse burial dug by a neighbor on a legit backhoe for less than $150. Last time I rented an excavator to clean out the pond, it was $500 for the day to get one delivered that had tracks almost 6' tall on it... pond cleanout went FAST! (but that was a rarity since guy with that excavator sold it) -- little excavator can be rented around me for under $400 for the day.
As a horse person, the implement I'd think you'd want most is a ABI Dragmaster (also called a Kiser Dragmaster). I have one. I LOVE it, but you'd need a bigger tractor for using one. The profile blade on the dragmaster does an excellent job of getting rid of hidden "ruts" in your arena and pockmarks from the horse hooves. When we ride western, we dig up our arena deeper, but we also ride classical dressage (sometimes) and it helps immensely to get rid of the hidden ruts under the fluffy part of the arena footing. We have a sprinkler system to wet the arena footing to the right consistency, but we sometimes use the water on the dragmaster to "touch up" the middle especially when it's hot out and lots of evaporation is causing dusting during the middle of a clinic.
You might want a manure spreader. My personal preference for a spreader is a tiny thing that fits in the stall aisle (so it can be parked outside a stall and loaded directly when mucking out. They're ground driven so you can tow with tractor or with atv or lawnmower or side by side or golf cart. I have a huge PTO driven one, but frankly I don't think I've used it in over 5 years. Even if the horses mostly poo outside, you still end up mucking that out of the drylots, especially with stallions or geldings who still think they're stallions and make poo piles to mark their territory.
For maintaining the driveway, I'd look seriously at a landplane. I very very seldom use my boxblade on the driveway since it's quite damaging to the compacted base if you're not careful. I use the landplane a few times a year (basically every time you notice some ruts get the landplane out and do the drive way BEFORE it gets bad). I prefer a 10' landplane for driveway maintenance but that would be too much for your tractor.
If you have to clear out ditches, I'd look at a six way hydraulic blade that's at least a couple of feet wider than your tractor (so you can angle the blade and it'll clear out the ditch past where the tractor tire is... if the blade is the same width as the tractor, then you'd need to drive in the ditch to clean it out).
My splurge item might be a snow blower or a three point wood
chipper. I don't have a snowblower since I moved to TX, but I really wanted mine back in Feb 2021. Yes, you'd only use it once every ten years, but depending on your driveway, your vehicles, etc it can make a pretty big difference in escaping down the driveway when you get a random snow of 12" that isn't supposed to happen. If you're comfortable driving on compacted snow on the driveway, then you can always just take the 4WD tractor for a few up and down the driveway trips and mash the snow down, but that leaves compacted snow that makes slick ice if you're unlucky. The wood
chipper makes fallen trees disappear into itsy bitsy chips that can be spread around pasture to decompose naturally so they don't have to be burned or otherwise disposed of...