OT - how to size/match multiple databases/apps for a single server

Hi List;

I have a client looking to host/co-locate multiple PostgreSQL clusters
(inclusive of PL/pgSQL application code) per server. I did some co-location
work several years back with one of the bigger telco's and remember there
were dire consequences for not carefully evaluating the expected resource
usage of each database/app and matching apps based on some common sense (i.e.
match a memory intensive app with a CPU intensive app)

My question is:
Does anyone have any templates, guidelines, thoughts, etc with respect to how
to eval and match multiple databases for a single server. Such as a checklist
of resource items to look at and guidelines per how to line up db clusters
that should play nicely together?

Thanks in advance...