The food or simply the cycle of rebirth

I want players on my map to have a limitation of the number of Wisps they start with. (Yes I use melee starting-units, 5 Wisps and 1 Townhall)
They will not be able to train more than 5 Wisps, but if 1 Wisp dies the player shall be able to train a new one, or "ressurect" them at the townhall for a goldcost. Howda heck do I do that?!

Is it possible for players to have a starting number of food without any buildings?
I want every player to have 20 foodsupply, regardless if they have any structures. Is that possible to make?

Perhaps you could hide a dummy units for each player somewhetre on the map, that would give the player the food supply.

There's a trigger for this I think. "Player - something"

About limiting the wisps, you should use an action that is something like
It is in the player section.