Reddit mentions of PostgreSQL 9.0 High Performance

I tend to find most books to be worthless. This one was very helpful: http://www.amazon.com/PostgreSQL-High-Performance-Gregory-Smith/dp/184951030X

PostgreSQL 9.0 High Performance is getting a bit dated but is still a good starting spot for understanding how Postgres works and utilises system resources.

It's hard to do server sizing without knowing how your workload looks like and performs, unless it's on the trivial end of the spectrum.

Are you looking at a fresh deployment or are you planning to migrate an existing database?

Probably picking up a copy of Greg Smith's book is a good place to start in that case. Keep in mind how things have changed with ssd's since that was published, otherwise it's all very pertinent.

PostgreSQL Admin Cookbook followed by PostgreSQL 9.0 High Performance

One of the best for learning about lower level details: https://www.amazon.com/PostgreSQL-High-Performance-Gregory-Smith/dp/184951030X

These are a lot of SUPER specific questions that don't really deal with webhosting in itself. I would definitely be looking into high performance postgresql as you're probably not going to get a lot of dbas here. This is implementation stuff, and it's mostly stuff that you're going to have to research yourself. There may be a web host that deals in what you're looking for specifically, I'm not aware of one but you may be able to find it.