Doubts about replication..

I have several versions of postgres 9.4.5, 9.4.4, 9.4.15 (3), 9.5.3
in different versions of Debian 7.6, 7.8, 7.11, 8.5 and 8.6.

I need to replicate the databases and I have clear that I must update all
to one version.
My main question is, Do you recommended me update to 9.6 or better update
to 10?.

Actually, is not the goal have high availability . I will use replication
as simple backup.
For reasons of $$$ I can only have 1 server in which I will replicate the 6
databases.

Do you recommend using a postgres service for the 6 databases?, or better,
I think, I must run a postgres service in different ports, for each
database?.

thanks in advance.
regards!
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