Philtre

Raccoons will eat berries, I don't think anything else will. So if your area doesn't have raccoons your berries will be OK, otherwise you probably want a fence.
When you harvest a plant growing on farmland, there's a small (5%?) chance of getting an extra seed. So you will very slowly get more over time. But the main source of seed is finding wild crops.
To get tree seeds, you need to break the leaves (your hand is fine, but shears speed up the process if you have them) before chopping the tree. You will get few or no seeds if you let the leaves despawn when the tree is chopped.

I think that as of 1.16, you now need to start sleeping before the storm actually starts.

If you put down an appropriate trough with food in it (small trough with grain for chickens, large trough with grain, veggies, or dry grass for sheep/pigs), animals who come within a certain range (28 blocks IIRC?) will move towards it. You can use a series of troughs to lure members of these three species into pits or fenced areas, so as to trap them for breeding or as an emergency food source. Animals will not despawn as long as they get a certain minimum amount of light, so as long as you don't try to keep them in a completely dark room, they will be fine.