Tell me how to set up a PG cluster where nodes can come and go as they like (for example without the need to reseed databases when they come online) in less than 30 minutes.
If you want to scale your system horizontally in 30 mins, you probably don't need to do it. It is fun in tutorials, but when you are dealing with tera(peta)bytes of data, you probably need to be more cautious.
This is just an incorrect assumption in my opinion. Say you are running on Microsoft Azure for example. There are no uptime SLA unless you run your service on at least two machines, because machines needs to reboot, be upgraded etc.
Also, if you take a look at perf when running PG on for example Azure or EC2, you will realize that IO is pretty slow but nodes are cheap. So you want to scale out early.
Running stuff on a single machine sounds like a perfect single point of failure to me. The actual size of the data does not affect wheter single point of failures are acceptable in a business.
I've seen so many people recommend PGSQL, saying its very simple, but when actually asked about how to set up a simple cluster which fulfills the absolutely basic requirements, then everyone just responds somethin similar to what you wrote. I find it very annoying to be honest.
