My friend does this, things she has done/had issues with:
dh is registered licensed too so she can go out and leave dogs with him
she does not have her own dog, this is a massive advantage that imo she doesn’t charge enough for as she mostly ends up with reactive dogs that wouldn’t play nice with others or very scared dogs.
You really need to consider space to separate your dogs from the visitors, your dogs might not like it either. We had a friends dog to stay here and billy pup was absolutely fine until it came to morning bed cuddles. I would make the downstairs the default for visiting dogs unless they become very unhappy and need the cuddles
friend and her dh are regularly woken in the night, fine for my menopausal never sleeps properly friend, less fine for your very important exam taking teens.
Her kitchen door was eaten in the space of half an hour when she left 2 small dogs alone.
You never know what you’re gonna get every dog is different and comes with its own unique baggage.
leave time for a deep clean in between each set of dogs
Dogs have different Houdini abilities, you need to be able to have several secure areas to separate them and an air lock kind of arrangement every time you open the front door.
book out your own dog free weekends/holidays at the beginning of the year and do not budge it’s a very popular commodity you’d be offering.
take a non refundable deposit every single time (unless it’s for me of course)
if you’re in Bristol they are trying to bring in plans to charge small businesses for using the parks, I can’t for the life of me think how they’d police it but worth bearing in mind.