During my first game, I depleted the berry bush pretty quickly and my little villagers starved while trying to figure out how to farm. In my second game I was more focused on getting Harvesting 2 early on so it wouldn't be an issue, but I've run into a couple more concerns later on:

1) Is there some technique to farming? It doesn't seem possible to support even a population of 15 with just the farm. The harvest cycles aren't long enough and the planting cycle is too long to keep everyone fed, I keep getting periods of starvation before the plants sprout again.

2) Does the berry bush replenish itself? I originally thought not, but just now a few new berries reappeared on its branches. How often does this happen and is it reliable enough to tap for food to supplement the farm?

3) Historically, people were hunting and fishing long before they figured out agriculture. What kind of islanders don't know how to fish?

1) Assign enough people to farming to get the job done

2) The berry bush will come around, so you'll be able to forage again

3) Fishing is obtained as the third level of harvesting...

In response to your question #2. If you are having trouble keeping 15 people feed you have two options.

1. Put two villagers on research, and put the rest on harvesting. You need to make sure you have enough food in the bin to last through the growing periods. For 15 people you will need around 1000 in the food bin. But the crops should be enough to feed the 15. Or;
2. Don’t have so many villagers until you get level 3 on farming. In the beginning while still on level 1, I’ll put three on harvest and two on research until I get over 500 in the food bin. Then I’ll put two of the farmers on research and the other on building the first hut. Then when I reach around 1000 in the bin, I’ll breed the builder until she has female baby.

Of course there are several ways to play this game, but this is the how I typically play it.

the berry bush on mine replenishes its self too... but the berrys dont show up again. the only way i found this out is cause villagers were carrying back berries from the "Empty" berry bush.