When I first started I felt the same way - I was doing well but could not in my wildest dreams imagine how I'd get 250,000 tech points to get some of the level 3s! It's a careful balanced between who is doing what, especially when your population is low. You kind of need to find out for yourself how many you need on harvesting and how many on research.

Keep in mind that villagers with higher skill levels do produce more too - so a master farmer might bring in more food than others, leaving them free to research. I also found that once my population grew and were adults and old enough to work, the food/research balance was easier to maintain. Every village is different it seems so finding who is best at what and making those choses are all up to you! Part of the fun of the game!