You might want to read through Starting a company that provide smart home automation solutions based on openHAB software, which was a fairly similar question.
In general, I’d suggest to also get some legal assistance when starting such a business. The key points were mentioned here: The EPLv2 license defines in detail what is allowed to do with the code and what obligations you might have. Furthermore, the openHAB name is a registered trademark, so it (= the name) must not be used in commercial solutions, while references to openHAB (like “based on openHAB”) are in general ok.
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