Without buying units

[Gatts]

There were threads on this forum about this option of gameplay, but mostly theoretical discussions, if or not it is possible. (It should be possible... )
But I do not remember someone finishing the game on impossible with this scenario... Most of the "unit containers" are for sell as well... So if the griffing king would have 30 griffing eggs... you would buy them or not?

Also I suggest to buy the spiders/snakes for sleem, as you won't using them in combat, it seems fine... I believe the point is not using bought units in combat... true?