1. Selecting the Synthetic trait does not seem to disable farming techs if you do not also select the Yor Tech Tree. The tooltip for the trait advises that both farming and population are disabled.
2. It is difficult to tell what the population cap is. The does not appear to be a reasonable upper limit to population with the Assembly project. This may be by design but there are not tooltips or techs that explain this.
3. When creating a custom Synthetic race with the Yor Tech Tree there does not appear to be a downside to selecting the "Infertile" and "Poor Farming" traits.
4. When colonizing planets, there is no downside to choosing ideology options that decrease population growth or population caps.