So, a respectable mid-tech unit might look something like a large body of
infantry, armed with basic kit, assault rifles and some nice wheeled
vehicles. Instead of big gun artillery, perhaps some heavy mortars and
mortar vehicles. Issue a liberal spread of anti-tank rockets and missiles
and some SAWs and a few interstellar barges.
Heavy armor is provided as needed by locals or other mercs. Air support
would also be provided by employers or other mercs.
I've actually been eyeballing some Peter Pig WW2 Germans as potential sci-fi
troops. MP44s work for ARs. Panzerfausts make good buzzbomb rockets and
panzerschreks can be worked in as guided missiles. Throw in MG gunners
porting their guns and SAWs. I'm even looking at using Early War anti-tank
rifles as sniper weapons.