I have been magento developer for over 7 years and have much experience in this field. I read your requirement and really interested, I built exactly this system before but in magneto 1x, it import products, udpate product price and stock and generate order xml data in a folder for another system to get, it doesn't hard to change it to magneto 2x version, I can start working immediately, I am sure I can finish it fast and make it work perfectly for you, please contact me to start it soon, thank you