I don't think your going to corner the market just starting out. Screen Printing, including DTG is a very large market.
Sounds like you don't have your own equipment, and are going to outsource your work, which is fine.
I think you need to get whatever quotes you can, but first get the customers to ask you for a quote. In the mean time find someone who does DTGs and have them give you a quote with their breakdown quantities. They don't have screens to charge you by color, but they might charge you a setup, and/or artwork charges.
Sounds like you don't have your own equipment, and are going to outsource your work, which is fine.
I think you need to get whatever quotes you can, but first get the customers to ask you for a quote. In the mean time find someone who does DTGs and have them give you a quote with their breakdown quantities. They don't have screens to charge you by color, but they might charge you a setup, and/or artwork charges.