FWIW, not only do we have my reef tank, we also have a small pond in the backyard and an above ground pool. So, I should be able to help think through this with you as I have experience with all these
Okay, so it looks like a either a steel or resin frame with a vinyl liner.
Home Depot's website says it's a steel frame but in the specs, it says it's a resin frame. If it's a steel frame (depending on how well it's powder coated or painted) there is some concern over rust from exposure to saltwater.
You'll definitely want to put some kind of padding under the pool to help insulate and buffer against any rocks you're going to put in there.
I can't find a reference to how thick their liners are but you might want to consider putting some pond liner down on the inside bottom of the pool to help ensure the liner doesn't get punctured.
It looks like at least some of their pools come with a filter. Which leads me to believe that there are bulkheads built in the liner which will allow you to hook up whatever filtration you decide to use. I'm thinking you'll want to use some sort of cannister filter since I can't wrap my brain around how you'd put in an overflow. As most small pool filters use 1" to 1.5" pipe/tubing you'll have to figure out a way to plumb it since hobby filters have smaller tubing. I'd have to see what you're dealing with to start thinking about how to do that.
Now, are far as equipment (IMO) that's all going to depend on the size of the pool (I didn't see any Bestway 100 gallon pools) and what you want to keep in it. So, let's start by deciding which pool you have room for and (besides the eel) what else you want to keep in it. Remember, eels are messy eaters so, your filtration will need to be pretty robust.