What make now that I have implemented a working prototype of my system?
A few points:


'open source' is just a sequence of two words without a well-defined meaning, you will have to dive into any real licenses that might exist for the exact products you use (likewise, Arduino is not a precisely defined concept!).
Your jurisdiction is always important.
You must separate the hardware aspects from the software aspects.
We are an EE forum, not a bunch of lawyers. That aside, there are people here that know quite a bit about the various 'open source' SW licenses, and people that have their own businesses.
The best way to 'productize' your product depends critically on the number of units you expect to sell and the amount of up-front money you are willing to invest. For 1's and 10's using existing Arduino's and shields is probably the best option. For 1000's you'd better design your own boards (or have it done by an expert) and have them built in China. In between it depends on a lot of factors.


My guess is that you can ignore the hardware aspects, except for the fact that the "open source'ness" of the Arduino makes it very easy for other people to copy and sell the same hardware.

The software aspect depends on the license(s) of the libraries that you use in your sketch. I think the Arduino IDE and compiler do not add anything to that (but the Arduino IDE built-libraries might!)