Hello,
I would recommend sending the prototype asap, don’t worry about an NDA as you’ve already filed a PPA. Save your money for a licensing attorney when they make the first offer.
And yes, your next steps are very important. Keep yourself on track and cross your fingers. There are a good handful of quality licensing mentors you can find online who’ve been in your shoes, licensed deals, and will help you for a small fee. So far you’re on the right track, good luck!