I find each set of bot production buildings (3 parts, 2 assemblers) supports ~80 bots comfortably.

I start by making the bot production buildings use bots to speed up the production, then only using them in their own haulers and builders huts.

Once their numbers are a bit higher then replace the injury prone industrial jobs and expand from there.

I also assign 1 or 2 more than required to each district, to help cover the breakdown gaps.