The only fully-auto wheat farm involves villagers, which autocraft wheat into bread in order to pelt each other with it. If you want a supply of wheat, you will have to resort to semi-auto designs or even fully-manual ones.
If you fill the farmers' inventories with seeds they can't pick up the wheat and so can't turn it to bread.
That means that you need hoppers, usually hopper minecarts, under the farm to pick up the wheat.
Villagers can only have 4 inventory slots with the same item so give them 4 stacks of wheat seeds and 4 stacks of beetroot seeds (in that order) and they should harvest the wheat and leave it for the hopper minecarts to pick up.