Now I can get 800 food points every time. I wonder what will happen if no one work on the cropland. Just let crops grow naturally.

Whenyou let a villager water the crops it seems to make the crops grow back quicker. Oh and by the way every time all the crops are picked, it takes longer for them to grow next time! So those crops aren't goining to save you forever!

That's not quite true. The crops appear on a fixed schedule, but if your villagers harvest them quickly you will have to wait longer for the crops to appear than if your villagers harvest them slowly. If the crops are not all harvested by the time the next crops are scheduled, any crops remaining unharvested will be lost.

Farmers gain skill when engaged in any farming activity, including watering the crops. Master farmers are an important asset to the game, so letting them water the crops is not a waste of time.

New Berries show up when the new crops show up. If you don't collect the crops in between new crops then your maximum is 800. If you get the food to the bin then you will have those crops plus the new 800. If you just wait until your bin is empty to collect the food, you could starve. You want to build up a reserve, especially if you leave the game on when you exit. Plus your villagers don't always eat enough. You also want to teach them to eat, because they can half starve with a full bin of food because, they don't eat enough when you are away. If you work them too hard and their health goes down but they are not officially sick you can bet them up to full health slowly by forcing them to eat drink water and swim in the lagoon. You can set them on nature walks to keep them from moving the boulder while your healthy villagers are in a time crunch. If you put a check by their name to learn a specific career while you are away they will get sick faster. I think it's about the whole free will concept. Now if you check a certain skill, make sure to check their health regular. If you have already taught them to eat and drink a lot, they don't get as sick even if you check the box.

But, watering the crops helps about as much as rain dancing. It does get them into the middle of the field on their own and you can nab them and dunk them in the berry bush. If you let them keep watering the crops they will water the crops 2 minute after the new crops and not even bother to harvest them. So you have to stop them from watering all the time, because they will contribute less for other things.
I think the crops would grow faster if we could use the pond water.

Also about the Farmers. The quickest way to increase levels is to get them to have improved skills. On their own like watering, is a slow process. Fishing is slow. In order to get the farmers levels up the quickest is to make them plant crops when there are none. It's the shortest skill because it doesn't have all that traveling. Also, they are closer to the food bin. They learn faster when they aren't hungry. So if you feed them while they are in training they learn to eat on their own and get sick less. Master Farmers are real stubborn and will act like they can't do other things.

Well, my policy is do nothing else until I get farming level 3. So now, all my 4 adults are doing research. All the tech points are kept except 6000 for farming level 2. They have no garden, lagoon or beach. Even the first hut isnt completed. Harvest is the only farming thing they do. Once the crops grow back, all the villagers turn to farmers and collect them all as quickly as possible. I believe food is the first one before people can fish, but the last one after that.

In the easy and medium games, I manage to get science tech first so they can get the other tech points faster, but that is on the premise that you don't go over-expanding your population. Usually though I have to do it on 1/2 speed because the tech points rack up at the same speed as normal or 2x, but they eat less often so the existing food lasts longer... they also don't age as quickly.
On the hard level I did have to get level 2 farming first, but then I was still able to get science 3 first and then farming 3. Getting the extra 50,000 points is quite fast with the speed of science tech kicking in

My first villager that died when I first started playing died of starvation and I had food.

Yes they do eat on their own, but, if you want to have a small group of people actually make it through the tasks and keep the original seven alive through more of the actual game you have to feed them. It's just about approach. I have 6 games going at the same time and I set different goals for each of them. Some of them take generations to complete the tasks. But if you feed them then you can take your original 7 further. Just a different approach. If they are in the habit of eating they actually go back to the tasks quicker. The ones that live on the survival rations...which the game seems to be initially set for will keep them alive, but they will get weaker faster. That's all.

I am probably spending way too much time playing this game.

I've played several games now, and except for times when a villager's health went into the "weakened" state, I've never explicitly taught them to eat. And I've played easy, normal and hard mode games.

I haven't yet had a game where an original villager made it all the way to the opening of the cave, but they've gotten pretty far and their first children have seen that event!