By the way, based on your experience, what Linux variants will you recommend for postgresql and what version.
I have read from severalnines.com site that CentOS 7 should be avoided as much as possible unfortunately I am currently running it.
I really appreciate your guide.
Regards
Zero reasons to avoid CentOS itself. It's a perfectly good server OS for whatever your needs. Unless you have a RHEL license, then of course you should use the Enterprise version you're paying for. What should be avoided is using the default PostgreSQL package that 7 (or even 8) comes with. 7 is still all the way back at 9.2, which has long gone out of support. For all RHEL related releases (CentOS, Fedora, Oracle, etc), use the PGDG repositories which contain up to date versions of PG for all of them.