I do the occasional short term boarder, mainly overnight stays but I have had a couple who came and stayed for a week while waiting for a hauler. I have 2 oversized foaling stalls that are totally separate from the main barn and an arena that is separated from all the other areas where I would turn out.
You're liability insurance will be astronomical. I pay over $7,000 a year for my home & ranch policy. If I didn't have a stallion and bring the odd mare here to breed, I would stop doing the short term boarding because I could drop the policy. Because I'm a breeding operation, I need the policy anyway and figured a few short term boarders would help defray the cost. And they do, but they're a lot of extra work.
My stalls are matted and lined for safety and I strip the stalls and pull the mats after every short term horse stay and then I spray the entire thing down with antiseptic solution and let it air dry. I wash and disinfect the mats, water buckets, feed buckets and anything else used on the boarder horse. I keep all those supplies separate from my personal horse stuff. I also have video monitoring for these 2 stalls, because of doing foal watch and so I can keep an eye on any visitors in these stalls to make sure nobody is looking distressed or gets sick.
You also will get horses that have not been trained well, are complete nervous wrecks and some that are just so flipped out by the whole process that they're fairly risky to handle. I notice those kinds of horses most when someone has bought a horse long distance and is shipping it home. They've been dropped off by one hauler and they're waiting for another one to come pick them up and finish the trip. Privately owned horses that come and stay for a night or 2, are usually not a problem because the owner will do 97% of the handling themselves.
It's a lot of work but having used a few short term situations when I've been travelling, it's a very welcome thing for a traveller to find. You do have to make sure they have the correct, up to date paperwork and look healthy.
I take pics at the trailer when they get off and again as they're being loaded. Just to be safe and I've had it stand me in good stead on one horse that was shipped here and waited a couple of days for a haul. The horse was skinny when it got here, was a flippin' loon and paced non-stop the entire time she was here. I took pics showing her condition when she arrived and recorded her weaving. Sure enough, when the horse got to her new home, the owner contacted me FURIOUS because the horse she got looked nothing like the sales pics she'd seen and the seller, of course, blamed the hauler and me. Because I had pictures of the horse coming OFF the trailer, skinny and poor condition and sent the pics and the video of her weaving, that took me right out of the loop for any litigation on that sale.