Latency wise it seems okay for llm training to put them higher than Starlink to make them last longer and avoid decelerating because of the atmosphere. And for inference, well, if the infra can be amortized over decades than it might make the inference price cheap enough to endure additional latencies.
Concerning communication, SpaceX I think already has inter-starlinks laser comms, at least a prototype.
If anything, I'd expect large-scale Mars datacenters before large-scale space datacenters, if we can find viable resources there.