There’s a level of control you have over the design. For something like a custom PCB with a microcontroller…if your asking this post your not going to be designing your own PCB. I’ve done it in college for simple circuits. Your prototype should be a “proof of concept” then you work towards the final version by making small improvements. You’re going to need to document your requirements very well and be able to have things like cad designs if you want an enclosure made. Custom PCB can get very expensive.

Man…what I could do with $3.5 million….im personally hoping to scrape together about 20k and I know I’ll be able to turn that into 500k a year…

Don’t charge $10 for an app, do a free version with ads?

You can have them build it how you want it. A mobile app with an admin panel website it’s just how much budget you have. However, the main thing is you will have to update your app at least every 1-2 years. Google and Apple will make you update your app to be compatible with the new phones as they come out. Two years is probably the absolute max I would give. To do those updates a developer would be needed