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!