Go for more acres over being “exactly right” in your planning. We have 14 acres, of which almost 3 acres is used by the house, 2 barns, driveways, yard space and a woods area. The rest of 11 acres, minus some double fence lanes, a wet spot fenced off, is available for grazing. I WISH I had about 5 more acres, but we manage nicely with the lesser quantity.
Our horses are able to be on free grazing for half the day, stalled the other half of the day in summer. Our pasture is excellent, very productive with regular mowing and fertilizing, even in dry summer years. Ground is almost 100% usable since we don’t have rocks, poor ground that won’t grow things,. This 11 acres includes a large outdoor arena, 100x30 meters, which horses graze on when not being used. I have it in 6 paddocks, which allows better use of the ground, better rotation schedule, so nothing is overgrazed.
We have between 6-8 horses most of the time, who are all grazed for summer food. They only get hay if hauled out to a show. They get some grain (less than a pound each) and wet beet pulp once a day, when stalled half the (24 hour) day in summer. None have any limitations on grazing, no hoof or other health issues needing dry lot care. Horses are large but easy keepers, not allowed to be porkers with regular work.
So do consider “how useable” the land you are looking at is. Woods are not accessible to our horses, they just kill the trees. Woods are a good windbreak for barns and paddocks horses are out in. Sure would be a lot of work to clear, for the tiny amount of grazing it would provide, as well as removing the cover to not look in the neighbor’s yard.
Ground that is wet, swampy, is probably not going to be greatly productive either, if water is on it much of the year. Check the ditches around any land. Deep ditches mean they drain LOTS of water from surrounding areas. We had to fix a tile line that drains our wet spot this year. Old line had broken, so that lowest field “appeared” to be full of small artesian springs after heavy rains! Made the arena need a day to dry out after such a rain. I spend EXTRA time in summer keeping those drainage ditches NAKED so they work effectively in water removal. I REMEMBER how deep the water gets when we get 5-6" of rain in 12-14 hours (up over the 60" fence posts in the lowest corner), so I want that much water gone FAST. I expect if you are on a mountainside, water will drain well even if ditches are not kept up. But we are on the high side of the river, so water leaves easily, we don’t get flooding that stays and stays. The well head is above any high water that comes, to stay clean. Things I never considered when we were looking at property, but would be high on my shopping list if we ever moved. One place we looked at had ditches over 14ft deep by the road, flat-as-a-pancake land, just on the other side of town. Doesn’t look very good in heavy rain!
Good luck shopping, go for bigger acreage over smaller. Up to you to use that space or leave it stand as farm develops. Go with smaller, but more paddocks, for better rotation scheduling. Land and grass gets a better rest with longer spacing of grazing. Horses do a better job of grazing the entire paddock evenly in smaller, mowed spaces. We keep horses in two bands so none are crowded, have less land impact running about in little (1 1/2 acre)paddocks, still have plenty of grass in ALL the paddocks of our small place.
Hope you find a nice place.