I do believe you can make money running a smaller facility. Whether or not you can make enough to quit your day job will depend of many factors. The foundation for setting up your business is still the same whether small or large and of course with only a handful of horses there is a very good chance you will need to find a second source of income. You will also need to have a good understanding of the cost to feed and care for five to ten horses and the upkeep of your farm year round. The cost to run a barn will change according to the seasons and weather and I believe it takes a good two years to get a real feel for what your cost are going to be.
I truly believe that writing up a business plan for a small facility is just as important as with a large one. It will give you a very clear view of expenses going out and income coming in for a projected period of time. Another huge part of the equation is your personal debt and business debt. What you owe on your farm, house or equipment is extremely important to your finances and profit.
I do know of small scale farms that make a nice income but they are able to charge a higher price for board because of the amenities and the many special services they offer. There are clients that are willing to pay a higher price for the extra attention that many bigger facilities can not offer.
The great thing about starting your own horse business is that you can design it any way you want and that is an exciting part of it!