Yes, make sure you're not looking at alfalfa or a hay mix that is loaded with clover
Unless somebody has enough money to plow up a big hay field and plant old time heritage seed, whatever any of us buys for our horses came from seed for cow hay
That would be the least of my worries but you can borrow a corer from somebody, take a few samples of the hay that comes off those fields and send it to equi-analytical. It's not expensive to have hay tested. Equi-Analytical Laboratories - Profiling Feed for Better Nutrition
Don't send it to the Co-op for testing; they only test for cows and the results you need for a horse aren't even in the same football field
Unless you are fortunate to have mucho dinaro, plan for the things that are a must first (barn, fencing, water lines, electric). Plan each of those as conservatively as possible while still getting quality contractors to do the jobs. Not always easy.
We have 23 acres and every bit of it was in perimeter fencing. We still managed to spend nearly 15K on cross-fencing and farm gates. We have 11 farm gates and several 4' gates.
Our fence is the standard 4" woven wire; I shudder to think what board or some other fancy type of fencing would have cost and the deer would have most likely pulled it over anyway
We've been here 11 years and haven't touched the woven wire, although the small pasture by the barn could use some tightening up.
After all that, if you have extra money for a big round pen or an indoor - wonderful