We share a fence. I can come up right to the horses and pet them. They are absolutely beautiful.
No----you can't ---- go right up to them and pet them.
Nor can you feed them. Do NOT feed them eve one tiny smidgen of a carrot or Apple, unless you want to make an enemy of the horses owner.
1. Most important you do not know if the horse has health issues that keep it from having sugary treats.
2. Some horses become nippy very soon, if they are plied with treats.
3. They are not 1,100 pound dogs. Respect the owner and the horses by staying away from the fence, unless you're mowing. If you're mowing keep the open side of the mower deck away from the horses so nothing flies out toward them.
3.1. Do NOT give them grass clippings. Grass clippings ferment quickly and can cause a horse to colic. Colic is a huge belly ache that can be dangerous if the owner isn't around to give the horse medicine.
4. To answer your initial question. You're going to have flies, no matter what. If the horse owner keeps their place clean, you shouldn't have any more issues than you normally would.
As far as smell -- well this forum is the wrong place to ask that question, lollol. We all think the smell of a horse is better than any perfume on the market, lollol