Frank wrote:

It seems to me I will be better upgrading my service (floor #1) to 300A
or 400A. This will allow some room to grow and why do it TWICE?


I currently have 3 meters with a single SE cable coming from the
transformer on the utility pole into a box that houses the 3 meters
with the individual SE cables for each of the 3 100A service panels.


Should I upgrade my service to 400A for first floor to cover all
current/future needs?


How do I interconnect them? I think I need switches inbetween the
meter and service panels but cannot find out how to set this up.

What you propose can be done but can get expensive. IMO, it's not a DIY
project either. One approach would be to build a 300 or 400 amp
service with two 200 amp main panels that would be supplied through one
meter from the power company. The individual feeders to each floor
could then be brought off the main service panels through circuit
breakers and sub-metered with meters purchased by you. I strongly
recommended that you involve your Power Co. Engineering Dept. and local
electrical inspector before doing any work, since they may want it
built their way, especially the grounding.