I doubt if anybody could give you a recommended setup, not knowing what you
are doing with this DB instance (how big it is, are you working with buffered/unbuffered logging,
are you working with a secondary instance (HDR), is this a OLAP like database (which might get loaded
over and over) or more a huge relational construction.
Do you have multiple instances running or is this a dedicated service, are you doing partitioning ?
How many parallel sessions do you expect, what amount of data will be changed in a specific time frame
(in order to define the size of the logical logs correctly).
The machine spec is also important, what type of storage are you using, raw or cooked setup,
amount of available memory, number of CPU cores etc.
BTW these questions need to be answered for almost any database setup, Informix 11,12,14 or
even for other database products such as Oracle, Postgres etc.
In case you have a running setup for a 11.x instance, read the release notes for upgrading, mostly
the parameters can be kept in the first step. In this case, check the old instance for bottlenecks
(duration of checkpoints, sequential scans, buffer usaged, shared memory usage), which will give you some hints.
When you have more memory available compared to an older setup, increase buffers as a first step.
When you have more CPUs available, increase NUMCPUVPS.