When should i go for the 3 village

If you have enough CP, you should settle it straight away. The low level fields in it will pay themselves back very quickly.

The return of investment is actually very important to notice. When you get above lvl 11, then the fields gets expensiv and it is actually more beneficial for you to get fields to 10 in other villages. Especially when you calculate the cp given as well. In generel all ratioes are better at low lvl buildings, that is how travian is build