How realistic is it to consider breastfeeding my 17 month old right after feeding my newborn? I didn't have much milk before and now with #2 I do.

Breast feeding for 2. That is amazing, God is providing you with enough breast milk for your 2 kids. It can be done if you can keep up with it, be careful, don't over do it, you have to take care of yourself, eat very healthy with plenty of proteins & drink enough fluids, you're eating for 3!, take your vitamins, your 17 mos old should suppliment with regular milk & solid food & start weaning . Good luck. Enjoy.