The install of postgres was relatively trivial, it did however raise many licensing questions and I don't think we even had a lawyer on retainer to talk through it. This also made it weird because of license reasons, we couldn't actually download and agree to the license because that would be our company 'selling postgres' as part of the package so we needed the client to do that step.

I can't remember exactly why HSQL/H2 wasn't used but I think it had to do with fault tolerance and redundancy and what we could do with postgres replication was preferred over what we would have otherwise used SQLite for.