I used to work at the Town of Mount Royal production facility from 1981-1993/4 (facility had moved to Ville St. Laurent by then).
P5000 came in two major types$ one was 8080 based, and the other was Z80 based. RAM on teh 8080 was 64K, 128K on the Z80. The Z80 was used on the "twin" (two terminal and two printer) version, and the Cluster (or 4 Head/4 terminal version).
Software was remarkably efficient$ copies going between the two floppies, printing, and editing all at the same time on up to 4 terminals, on an 8 bit CPU and 128K of RAM.
As far as I know, the software was originanally developed in Ottawa, lead by the person who would become company president (went to school with Dr. Wang). Company started as Micom, and was eventually bought by Philiips.