As amazon xenoplague, basically you should familiarize yourself with some mods that only affect xenoplague units.
This may come as quite a shock because the game doesn't specifically mention it. But other units which is made xenoplague through mods are also considered xenoplauge. This is the key.
So early on, the easier way is to use lancer with the xeno parasite (and plague bomb if you can afford the cosmite). The reason is your lancer can self heal themselves with those bomb if they are made xenoplague, and if they are close to enemy units also stagger them (if they are not immune) and often infect them with parasite.
Support from arborian sentinel is very nice too, as it can give shield to your lancer.
Pustules can also be used in the same way as lancers, they just need to carry plague bomb, and if you can affort it xenograft.
Basically there is a one mod and two mod variant of this units, the main force of yours in very early game should be around this. 1 mod variant, non xeno close range units should have xeno parasite, the xeno one carries the plague bomb. 2 Mod variant, for non xeno add the bomb or xenograft (up to you), for xeno units add xenograft.
The reason why there are 1 and 2 mod variant is because of the cosmite cost. If you are lucky with the cosmite rift near your starting locations, 2 mod variant is good. The 3rd mod is flexible, for example if your lancer need the grounding mod, then use it if not you can grab xenograft.
Biomancer is a must, at least 1 per stack is a good number. For their mods, you can put whatever you think best.
If you tech rush to plague lord, preferably the latest is at turn 25, so try to get it before turn 20. Leave independent or marauder stack with 6 units in it when you haven't have the plague lord tech, the reason is you want to save this to sling shot few to several destroyers to plague lord as fast as possible. If i recall correctly there is a strategic op that debuff entire stack with parasite infection, this is very good for that.
It's quite possible to have 4-8 plague lords by turn 20, if you are lucky. Which at this point, there is little in the game that can counter it, the AI especially can't do anything.
For late game, you may want to create two type of stacks. The 1st type is comprised of all inherently xenoplague units, the other is non inherently xenoplague or rather artificial xenoplague. The hyper aggresion mod is crucial at this point. In the 1st type, any xeno unit can carry it because the 1st type just consist of plague lords (or lesser evolved xeno units which will evolve to the lord anyway), just need one unit per stack to have this mod, more is a waste. For the 2nd type, biomancer is arguably the best candidate, because you don't need many of these, they are just there mainly to provide scans, and rarely backup heals and sleep. The 2nd type will consist of bombardons, tyranodons (either the unit version or hero mount version is fine), arborian queens, and 1 biomancer. Against the AI, all units from both type of stacks can just put blood fury inducers, xeno parasite (or its upgraded version), xeno proliferation, then just auto battle everything at this point (watch out for the oathbound though, somehow the AI is very good with it in autobattles).