So here's the first crack at a Marine and Knight army. It's very in your face. The plan is to over load with threats to mitigate the fragility of the Knights to ranged firepower. Here goes:
Chapter Master: Artificier Armour, Shield Eternal, Thunder Hammer, Auspex 240
Tigirius 165
Tac Squad: plasma, combi plasma, Rhino 130
Tac Squad: flamer, combi flamer, Rhino 120
3 Centurion Devastators: Grav Cannons, Omniscope 260
Tau Commander:
MSSS, C&CN, PEn Chip, VRT, 140
6 Firewarriors 54
Knight Errant 370
Knight Errant 370
So mini Gravstar supported by 2 Knights. Troops start and huddle in reserve. Everything is pretty fast if Tiggy gets gate. Everything can fire at 2 targets a turn. Get up close do lots of damage. Assault with the Knights, profit