Given that yours is a primarily visual product, I'd spend most of your social media efforts on Instagram, where you should do your best to follow (and in return get followed by) gallery owners, art dealers, collectors, museums, curators - anyone of influence in the art world - especially those that display a preference for the sort of work you do. Facebook ads wouldn't be a waste of money - the FB user is skewing older, so you'd be able to establish contact with more established potential buyers. But because Instagram is so visual, I suspect you'll get much more traction there.

Also, a still-life artist I know gets great traction on FB by posting time-lapse videos of his works in progress, which could also be utilized for Instagram and Twitter. Presenting yourself in a friendly, accessible way will also go a long way towards establishing a connection with potential buyers.