The six-part series you are looking for is The Sand Wars (1987-1990) by Charles Ingrid. It matches all seven of your criteria perfectly. I read them when they first appeared in the late 1980's; the story is a quick read, but I enjoyed them as a younger man and recently re-read them many years later and found them still a good read. Brief synopsis from ...
1900: In The Struggle for Empire, by Robert William Cole, Iosia is a planet of an unnamed star somewhat more distant than Sirius:
For a long time past, a band of adventurers had been
colonizing a planet called Iosia, which was situated
far beyond the confines of the Sirian System.
The Struggle for Empire, Chapter III: The First Note of War
This planet is ...