I think Z is the smallest practical Modeling scale, with N being a good bit better, .......just my tupence............

That said, not trying to completely deRAIL the dialog here, I once considered TT (1/120) a reasonable/practable size. I went with N, because there was just no viable availability/selection of TT.

I have modeled in, O, S, (teens) HO, N & Z; currently mostly N (Nice/Normal), then some Z and very few HO pieces. The best modeling scale I have actually Worked in is 4' 8.5" gage, aka 1:1 as a switchman on the NYC. I find the customary modeling scales a bit SAFEr. MY stint as a NYC switchman started with, just learning & practicing Properly getting on and off moving trains.

I have never even seen a T scale/gage, live and up close, pictures only, but just having some Z makes me appreciate just how BIG, N scale or PS (Postage Stamp) is.

While I have partly DERAILED this TRAIN of dialog, this is a siding only slightly divergent from the SIZE subject main-line.