I also recommend doing CMYK only if just starting out. It allows you to learn the machine, and any errors from learning and experimenting are cheap to fix.
White ink is not really for a hobby shop or one shirt every couple days. Using CMYK only(dupont), you can get away with only doing a couple head cleanings a day if not printing.
Marketers sell the white ink on dark shirt because it is a big WOW factor, and gets the sale. However, it is not really a viable option for a noob or beginner with no business coming in.
DTG is very profitable once learned, but it does take effort.
I 100% agree with this post. White ink is in no way profitable for very low volumes of printing just a few white ink shirts per day or week.