Thanks!Weed management in the pasture is a whole different ball game. Depending on the weed and how much is present and whether it has seeded (and next year you will have even more) or not, or does it also spread under ground. That will determine what you have to do to control it. If you have to apply chemicals then the horses will need to be removed for a time. If you are disking and burning then you have to allow time for reseeding and new grass if a large area or surrounding grass to fill in in small areas. Some areas you may be able to hand pull. Again it all depends.
I get the feeling you are new to all of this. I'd suggest you find a copy of Cherry Hill's book about keeping horses on small acreage and get to know the county extension agents. They should be a wealth of info for your specific area.
Same with fertilizers and same with overseeding. Dividing the pasture helps 3 to 4 sections with a dry lot is a good place to start.
Number of bales would be an estimate based on the weight of your horse/s and the weight of the bales. Then you adjust for how much they actually consume.
For every 1,000 pounds of horse I expect to go through 20 pounds of hay a day if there is no grass. Some of mine eat more, some less and amounts depend on how much grass is actually available that they are eating.
In winter I typically go through two 1,200 pound round bales a week when I am at maximum capacity for my pastures. That would roughly be 50 squares a week. That drops in the spring once grass starts coming in and depending on temps and rainfall I may not have to start putting out bales until November. Some years it is October. In a drought year it may also be all summer.
Rounds are cheaper but storage and moving can be an issue if you dont have the equipment to haul and put out as well as store.
If I have a good cool season grass established I can cut that in half. Here rainfall is abundant in the winter so establishing a winter pasture is not a problem. All of your costs are mostly up front as opposed to hay which is purchased as needed. But that can also depend on your area. Some places if you don't buy to fill all your needs you risk not having hay. If you buy for the entire season you have to have a place to store it.