You don't need anything like that amount of yeast. I make bread all the time and I have a sourdough starter in the fridge which I made originally some months ago. Since my husband reacts rather violently to sourdough this is my secret pleasure - I make a loaf occasionally, slice it and freeze most of it for breakfast toast.
When I make ordinary bread, I put 1/2teaspoon of yeast with 250ml water (or whey when available - one of the great spin-offs of cheesemaking is the whey which is a great addition to bread, soup,....) and 250gm flour in the breadmaker and run the dough program. Then add the rest - my usual recipe is another 250gm flour (whatever sort takes my fancy on the day), 1tspn. salt, 2 tspn. sugar, some milk powder, and an egg, some linseeds, whatever, and run the dough program again, make into rolls or a loaf and bake in the oven. Faux sourdough.
My sourdough starter is a pure rye - as I'm at the coast and the bread bible is at home I can't remember the exact ingredients, etc, but it was the usual drill of mixing wholemeal rye with water and refreshing it daily for 4 days (no added yeast at all). I've made pure rye bread using the starter and it's great, if you like rye bread. The starter is very noxious looking but comes to life amazingly well even after being neglected for weeks on end.