what percentage of starter should go into the final dough?
Depends on what kind of dough you're making, and what you're after in the final loaf.
I would suggest:
Mostly white dough (a combination of bread flours, whole wheat, spelt, etc.): 15% of total flour weight
Multigrain dough (mostly bread flours, but with whole grains bogging the dough down): 25% of total flour weight
Rye dough (more than half of the flour being rye): from 30% to 40% of total flour weight (preferrably from a rye sourdough).
When you say X% of total flour weight, does the total flour weight include the weight of of the flour in the starter or exclude it?
Does it matter what hydration your starter is for these percent guidelines to work? If yes, what is the hydration of the starter?
Thanks in advance
that's in your starter for the same amount of flour in the regular recipe, so if the recipe required 300g of flour and you wanted make 15% of that starter, you'd calculate enough starter to add 45g of flour, and take 45g of the required flour out of the recipe. (300 x 15% = 45) So you would then use 255g of flour from your bag plus 45g flour from your starter to get that 300g total flour in the dough.
The hydration won't matter, as long as YOU know what it is so you can figure out how much starter you need in order to supply X-weight of flour.
Let's assume it's a 100% starter; to add the 45g of flour in the above example, you'd add 90g (it's half flour, half water by weight). You'd also need to reduce the water/liquid called for in the recipe by 45g.
If your starter is higher or lower hydration, you need to adjust how much water comes along with that 45g of flour in the starter. So if it were a 125% hydration starter, you'd need 101g of starter, of which 45g is flour and 56g is water. You'd therefore need to reduce the water/liquid called for in the recipe by 56g.
Just what rainbowz said above, i.e. total flour weight is the weight of flour in your ripe sourdough and in the final dough. You need to adjust the recipe to the hydration of your starter, so that the total hydration remains the same. The starter hydration might affect how the dough behaves (extensibility vs. elasticity) and crumb profile, but the percentages I wrote above does not depend on level of hydration.
That sure was quick. Thank you for an excellent explanation that answered both my questions
===== edited ==== to include a thank you to hansjoakim also, whose reply appeared two minutes after my original thank you was posted.
You're both great. Very helpful guidelines.