Hi, I can help you to build this windows program. I'm experienced developer in this field. Please check my opinion about your highlight.
1) To make the device plug & play, need an interface that will translate the sensor signal become serial use (I prefer I2C).
2) The data will be store in mongoDB or another no-sql tech.
3) For the reporting, I will build as a web app using PHP.
4) The concept to able to add more device and plug & play is to make each device has like an ID inside. So the admin (with web app) will add this ID become a device by mapping it with master data (Kind of sensor, unit, etc).
5) Case will be from plastic material. We can choose a transparent one if it measure light.
6) Yes, but tt's base on case design.
Please consider my bid and I hope you can talk over chat.
Regards,
Teguh