Investing in "small towns" is actually a very broad term. Some people call small towns those with 70,000 people, others those with 10,000 or less. There are small towns that are just 20 min outside a larger city, so the town is small but an easy commute to a larger city for supplies and jobs. Then there are small towns that are more than an hour away from larger cities, so not commutable and Home Depot is more than an hour drive away.
Some things to look at are what is the job source for your tenants? If you are close to a larger city then that can be your job source. If you are far away from a larger city, is there a major employer that is a significant portion of jobs and if they close down will that have a huge impact of that town? I have a number of properties that are on the Oregon coast in towns that are 10,000 people or less. I am not worried about any major employer as tourism is the major employer and people will always be wanting to be close to the ocean.
As far as financing goes, I have been told to look at the local banks as they want their money invested in the communities that they are in. I have not had to do that yet.
Getting good contractors at decent prices can be a challenge in small towns if you are not close to a larger city. For example; I recently had to deal with a sewer line backup. I called every company in town to get someone out to cable or hydrojet the line. They were all booked up and it took me 5 days to get someone out there. In major cities I can get someone out for emergency service typically same day, even if I have to pay overtime for after hours work. It is not possible there. I am lucky that I can and like to go to my properties and do most of the major renovation work myself. It saves me a bunch of money and time.
In one of the towns the only hardware stores are Ace and True Value. In that town none of them are open on a Sunday, so the closest hardware store for an emergency on a Sunday is 1hr 20 min away. I make sure that when I am doing major work that I plan to avoid potential problems on a Sunday. ie I am not replacing valves and faucets on a Sunday in case something breaks and I need to shut off water and go get a new part to fix it and they are all closed until the next morning.