Echoing others here, make sure you can lock access. We have similar aged kids, they are capable swimmers. The biggest thing your pool will do is give them practice, and practice is what's needed to give them ability.
We don't let kids swim without an adult. Our pool is fenced in. During the summer I'll sometimes sit by the pool with my laptop and keep an eye on one of the kids swimming.
We swim a LOT, I keep an eye on everyone, but I know my kids swimming ability level. When they're tired they rest, that's the biggest danger, swimming into exhaustion. My bigger concern isn't my own kids, but friends. My kids know not to jump close to walls, not to do stupid things. Friends...ugh... if friends are swimming I'm either in the pool or right next to it. Too much stupidity from friends who think that since a pool is in a yard there aren't any rules verses a public pool with written rules. I purchased a sign with printed rules and hung it.
Make sure you're consistent with whatever you tell kids/friends. Both our kids and their friends abide by the same rules. My kids don't get to run while friends walk, everyone walks.
The auto-cover isn't a bad idea for summer.
I'd highly recommend a loop-loc cover or something similar in the winter. They cover the pool and are secured by bolts in the cement. You can walk on it and it'll flex, but you won't fall in. I tested ours, I walked out on it and confirmed it held me. This was a life-saver because a month ago I was working in the pool area and the door didn't close all the way. Our 20mo old discovered this and bolted into the pool running right onto the cover. He just stood there as he sank and his feet got wet. If we had one of those tarps it would have been a disaster.
Our fence has an auto-shutting door as well. I need to WD-40 the hinges for the summer, but most of the time it works really well. So well that it's annoying because it closes so quick.
