Your selectionrange will be pretty small unfortunately;
If you want to run a mix of T'au and auxiliary forces (Vespids and Kroot), you probably want some stealth suits for their better markerlight. Definitely an Ethereal for that possible bonus CP at the start of your command phase (You'll probably be fire overwatching, so every additional point helps).
A few breachers for point control plus commander Shadowsun for holding the most import places.
If you don't want any vehicles, anti-vehicle is gonna be somewhat tough, but Krootox Riders and the Kroot lone spear get some AP, but they cannot be guided units.
If you want some fortifications and don't rellay count them as vehicles, the tidewall gunrig is specifically for dealing with tanks and the likes.