FoundationDB is not easy to set up. And it ships with near nothing out of the box; you have to build layers atop it's foundation to do nearly anything. But the polish is through the roof and it's one of the least likely systems to turn into a live hand gernade on the planet.

Etcd is a quite excellent piece of technology that is actually, relatively speaking, quite easy to set up, is quite polished, has few all in all drawbacks. It's great tech. But software alone isn't going to change the fact that you're operating a distributed system.

The biggest problem, in my view, is that there are so few opportunities to get any real experience with most of these systems. You kind of need to be running thousands of decent sized instances all at once to begin to appreciate the weirder sides of what could happen & what you need to do in response. For most people, many of these distributed db systems operate just fine. Until one day they don't, and then they are totally hosted & either suffering extended outages, rollbacks, or worse. Simple things like node rotations usually go smoothly, but don't generate the same kind of hard-fought experience. Your ask about starting out feels like it's asking for the safest most secure route, but only battle hardened rainy-day ordeals are ever going to actually get you to a place of comfort.

Hence... maybe just use postgres instead.