We know what OPT is. However, the point of it is not to draw out your US presence while you putter around on other activities. You're expected to do your training and leave.
OPT can be pre or post graduate...
OPT - Eligible students can apply to receive up to 12 months of OPT employment authorization with how that is used up calculated pre and post grad) if a STEM dregee he could have 24 month on top of that under given and largely easy to meet conditions. The hour requirements whatever the case are extremely flexible.
The OP starting a business (or otherwise earning foreign income) in his home country appears to not bar him from OPT.
If anything engaging in these business activities testify to the OP's nonimmigrant status.
Of course like anything immigration related in these times, the OP needs to confirm this with an immigration lawyer because of the new strictness on any overstay and on visa conditions.