My default for me is always 80, and sometimes 30-40 trade units will replace gold miners when gold runs out and when I need population.
that will depend a lot on the map, civ, opponent civ, if it’s team game or 1v1.
In general you want to have at least 100 vils (with civs like mayans, aztecs) up to 150 (if you want to afford expensive techs like siege onager, paladin, etc). Generally I don’t stop producing villagers until I reach 200 total population
The answer is always “It depends”.
A total 1 TC push = Maybe only 60.
3 TC or even more TC boom = 120+
2nd and 3rd TC added later = Barely 100.
Hence the name? TwerDefender? You just wall and tower until 200 villagers?
it depends, right? I usually produce army at the same time, so I tend to cap out around 130-140. fewer when playing against the AI

I don’t stop producing villagers until I reach 200 total population

You just wall and tower until 200 villagers
200 pop ≠200 villagers