Disclaimer: I am not a professional electrician.
@Sylvia B. Are you sure that's the breaker box? That sort of looks like where a meter should go. On the other hand, the meter could be at the pole - off to the right in the picture above.
Another possibility... in the real estate listing for that house, it looks like there is a little workshop/garage/something back behind the main house. It could be that the box on the front porch just has a couple of breakers in it - one big one (like 100 A) for the main house, and another one, possibly smaller, for the workshop. Then, the house and workshop would each have their own breaker box, with all of the branch circuit breakers. If that's what you have, then you probably don't have to change that box on the front porch, unless you are upgrading the entire electrical service from the utility (like, going from a 100 A service to a 150 A or 200 A service). You might need to change the breaker boxes in the house or the workshop.
It isn't unheard of to have the breaker box outside, but usually it happens where the weather is better (drier) than southern Missouri. I have seen it on houses in Arizona before. The sheet metal of the box is built a little differently, so it can stand being rained and snowed on, but the breakers that go inside it are the same as any other breaker box of that same brand.
If that box on the porch is the one and only breaker box for the whole house, the only thing I would wonder about its current location: is it possible for somebody to actually operate the breakers in it if they're not real tall? It looks like you'd have to stand on the porch and lean over, or stand on the steps and reach up.
As the electrical code gets newer, more things are required to be on their own circuit, and in the newest code, some things need special breakers (bedrooms on AFCI breakers). If the panel that's there is a well-known brand (like Square D, General Electric, or Cutler-Hammer) and has a few extra empty spaces in it, you might be OK with re-using it; you'll easily be able to get new breakers that fit it, and there is space for them to go. You might have to install a bigger conduit from the breaker box into the house, if the conduits that are there are fairly full.
If it's an oddball brand, or if it's nearly full, then you might have to replace it... if you do that, you should at least ask the electrician about the pros and cons of moving it inside.
Disclaimer: I am not a professional electrician.