Is their the effective layer limit for a Geoserver instance running on Ubuntu Linux 16.04? I assume that each layer translates to a Postgres table, and while I have read that there is no real limit by Postgres on number tables per instance, there are some limits imposed by OS and performance considerations. What count of layers in GeoServer might you begin to experience performance problems?
I don't think there are definite answers, but in terms of layers numbers there is this GeoServer Improvement Proposal giving some numbers:
and then this thread:
Long story short, if you are using GeoServer 2.12.0 on-wards, you are probably fine handling < 50000 layers (note the benchmarking machine was 8 years old and using a spinning disk, using modern hardware you'd get better results).