does it work for Terpish? if it does, then that's all it needs. (how are you going to feel if you change it as "unrealistic", and then a month from now, someone describes a Real World language whose tone system is exactly like what Terpish's was?)
That seems somewhat unlikely based on what I have seen so far, since the processes I had in mind for Terpish so far seem unprecedented in the natlangs at which I have looked. It would appear that tone tends to work quite differently than what my intuition woulod suggest, and many accounts of tone sound quite counterintuitive to me. Although having a tonal system identical to some real world language raises the opposite problem of making the conlang too derivative. It really is a challenge, I think, to balance the competing demands of originality and naturalism.
I have been looking for other polysynthetic languages with tone to get some ideas on how they handle it. Chinese probably has the most studied and well-known tone system, but its isolating grammar and prevalence of monosyllabic morphemes make it less applicable to the Terpish situation. Vohpenonomae sent me a paper on Cheyenne tone rules which has given me a starting point. I have been looking at some others here and there, like Arapaho and the Bantu languages, that have similar properties of lengthy words and complex morphology.
It would also help to consider where tone originates in the Terpic languages and what implications that could have for the tonal system. I am thinking that the high tone originated on syllables which ended in glottal stops derived from eroded final consonants. That seems pretty well attested in natlangs, although it could result in most words lacking tone unless coda consonants occur pretty regularly. It does raise some interesting possibilities like suffixes which induce high tone on the preceding syllable because they historically began with glottal stops.
"There was a particular car I soon came to think of as distinctly St. Louis-ish: a gigantic white S.U.V. with a W. bumper sticker on it for George W. Bush."