The biggest thing I'd emphasize is, don't full clear grass if you're farming hay. Don't let animals do so either, have at least one grass field apart from them entirely. Grass begets grass, so the key to efficiently harvesting it is to cut out little chunks all over the place, so there's plenty left spread out which can quickly fill in the gaps. Large fields of nothing but grass won't spread anywhere but at the edges, so instead, make it like swiss cheese, and repeat the process as the holes fill in.
Of course this only applies if you care about them eating fresh grass at all. As indicated, at 50g per animal per day, just buying it certainly works as well, and leaves the rest of your farm clear to do other things. If money isn't an issue, you can do what I do, and have a chest full of hay (hundreds or thousands of hay) next to a silo, and shove more in there once every X days (once per week per silo is my typical schedule, so if I had 2 silos, once every other week). That way you can just buy a few hundred or thousand more hay from Marnie when convenient, shove it in the chest, and not worry about it.
Whatever you do, I'd definitely not recommend just letting them starve, the animals output more than enough money to cover the cost of hay, so they've definitely earned a meal every day! Hope everything gets sorted out!