And here I thought I'd read the primers! Sorry about that.
Anywho, before I embarrass myself further, I was indeed considering using Saurus Warriors from Warhammer Fantasy as the base model; the results I've seen on the threads Babaganoosh (fantastic conversions by the way!) provided look very awesome indeed, while being in keeping with the descriptions of Tarellians that we've been provided with. Duredhel's pictures of Tarellians
are generally what I think of first when I consider them mentally, thanks to the Lexicanum, so again Saurus Warriors are rather in keeping with what I have in mind. Once I start the project I'll be sure to start up a thread about it in the appropriate subforum.
My main issue currently is trying to balance a combat-orientated unit in with the primarily shooty-shooty Tau. While helping to provide a more effective close-combat alternative to the kroot, the Tarellians should feel like a Tau unit and should not make close combat a viable tactic. Essentially I envision the Tarellians as providing an effective team for absorbing charges and tying up close combat units while Firewarriors can move around them. Maybe it's just my poor tactics, but I find kroot tend to be too fragile and require careful positioning and movement. In agreement with Shasocastris, if I make the Tau strong both in shooting and assault, then I'd consider my Tarellian unit to be a failure. It has to fit in, it has to compliment.
Given the rules regarding custom units, I may instead use this thread to discuss fluff rather than gameplay mechanics. As I cannot yet post in the Library, I'll post any background writings for Tarellians within my sept here for analysis. As they're a species we don't have a lot of information on, it should allow me a fair bit of creative leeway. If I create my sept effectively, it should provide an original, or at least entertaining, look at an alien/Tau force while fitting in with current lore.