I think they can only be harvested from fields in the autumn. Sometimes the filed returns the wrong crop, especially if speeded up by ads. Best advice would be to keep the game running while five people harvest the crop and don't restart - that is until the game gets patched again. Harvest as many as you can in autumn because they are needed in most cooking. No harm in using ads to make a dish if you don't have spuds though, that works fine.

I'm not sure if there's any benchmark for success at any particular level that you have to reach. Generally just keep building and upgrading the sleeping shelters. They should arrive one at a time.

If you build it they will come. Create additional sleeping shelter. Nothing happens until then normally, then usually after level upgrade.

Reasonably advanced civilisation. No trees left on the island.

Early version hacks - edited