First few years, we used two professional innsitters; now work with two local ladies to fill in when we are on vacation. In 2017 that was a total of 8 weeks (daughter and new baby in France)! Usually we vacation in "shoulder season" so as to not have things too crazy. We like to handle wedding weekends, graduation, etc. ourselves Innsitting worked very well, we got favorable reviews from their tenure. It pays if you have enough guests: we actually netted enough money to pay for our trip to France.
Key for us was the cost to pay a professional innsitter stay when we had no guests, typical of "shoulder". Professionals came from far away and it wasn't practical to have them go off duty; the local ladies are happy to go home for a few days if there is no one at the Inn so they can garden, feed dog, feed husband.
So ... I advise you to start local. Look for inns within an hour's drive. That lets you meet face-to-face to build confidence with a potential customer and makes it easier for you to be flexible in response to varying demand.
We have several innsitting members on innspiring, and they may also advise. We have had some controversy in the past about the subject with some very protective innkeepers (remember "rocket science" y'all?) who could never trust their baby to a stranger. But if you can make a tour, to meet up, bring a physical scrap book with photos from your glory days showing your beakfasts, your reviews, level of housekeeping. Use a pitch that you can be there in a pinch, as a lot of innkeepers really lack a back-up plan for illness, out-of-town family emergency, etc. even if they are too hard core to actually take a vacation themselves.