volume of starter

You should build successive batches to get the quantity you want. 

Here's a general example, 

First Build 

• 1c starter
• 1c water
• 2c flour

Let rise until at least doubles, up to tripling...however long it takes to do this (could take 4-16 hours).  

Then you should have about ~3c starter.

2nd build:

• All of first build
• 2c. water
• 4c. flour

Let it rise until at least doubled (up to tripled). You should now have 6+ cups of active starter, with enough to innoculate another build.