Can h4 visa holder start its own small business like botique ?

No. You cannot. That would be an activity in violation of the terms of your H-4 dependent visa status. If your country has a Treaty with the US, and your investment into the business will be at least $55K (if filing with USCIS) or $75K (if filing with consulate abroad), then you could look into preparing an E-2 Treaty Investor visa application.

Slight disagreement with my colleague only on the amount needed to obtain an E-2 visa. It really depends on the business. I have clients who invested far less and successfully obtained E-2 visas. Definitely don't try one without an attorney though.

No. H-4s cannot work whether paid or unpaid.