Hello,
I've been developing for Unity for about 5 years now. Last year I have worked on Unity PC game Kursk, before that I have delivered a few apps and games on Unity as a freelancer (I have personally done modeling, coding, design for those).
Passwords for doors is pretty easy to understand, so is inventory system. For the PayPal integration are you looking for just plugging it in, or for developing an in-game storefront that uses those transactions?
Kind Regards,
Piotr Lugowski