Here is my Tech Level upgrades for Isle I. I change my Tech Level Upgrades in every game.

Harvesting Level 2 (always a must)
Harvesting Level 3 (my little experiment)
Building Level 2 (need to build more huts)
Medicine Level 2 (needed to extend life of villagers)
Fertility Level 2 (needed to shorten time of maternity leave)
Spirituality Level 2 (my villagers are aging)
Medicine Level 3 (given by random event)
Science Level 2
Science Level 3
Building Level 3
Spirituality Level 3
Fertility Level 3