Greetings,
Interesting project indeed. I am assuming this will be a battery powered rechargeable device - which means the circuit needs a lipo/li-ion, charger, dc-dc, BT controller, flow sensor. And since it's a portable device - there must be size and battery life requirements too.
It involves schematic, layout, firmware, manufacturing & assembly, board bringup before you can have your working protos.
I have good expertise with these things - please see my portfolio for details. I can help you here. However would like to discuss details with you. Also please note that my bid does not include the hardware cost.
Look forward to hear from you.
T & R
Alok Pugalia