Re: reliable energy. Even in low earth orbit, isn't sunlight plentiful? My layman's guess says it's in direct sun 80-95% of the time, with deterministic shade.
Depends on your orbit, but you need to be prepared to rotate into Earth's shadow seamlessly.
It's super reliable, provided you've got the stored energy for the reliable periods of downtime (or a sun synchronous orbit). Energy storage is a solved problem, but you need rather a lot of it for a datacentre and that's all mass which is very expensive to launch and to replace at the end of its usable lifetime. Same goes for most of the other problems brought up