Spoiled for space...
This sounds awesome! definitely let me know how this goes. We have a lot of people doing "counts as" armies and modeled armies. The Manager of the store I play at runs a Mech guard army.. but with Orks. Most of the tanks are kustom built. Another guy runs Tomb Kings as necrons, but that's kind of expected. And my other friend has a "Sisters of battle/Gray knights army" which... is basically a Tau force with "chameleon suits". They have the guns and everything. I think my favorite was a D&D mini he made if a knight errant with a shield and sword... as a shield drone.
EDIT:
well... that kind of depends on what you want to do with it. Firewarriors have the best Rapid fire gun in the game... But kroot are terribad. Only good use as a speed bump.. and you can do the same with piranha drone drops. I suppose it could be a strong enough list to play if you took hammerheads and were willing to use lots of drones. I'm not super familiar with tau codex.. but if your leader isn't a suit does that mean he has to be the ethereal? I don't know if there is a 3rd option...
It also depends on what game mode, terrain, and what army your facing.. But honestly .. why would you want to take that kind of list? The mech suits are by far one of the best units (if not the best) in tau. The Jet packs and massive firepower are ridiculous enough as is, let alone the ability to target separately.
-Wrath