i agree with doganjo, get a good business plan together, this will help you as you go along, and give you targets to aim for..
think about what will make your art gallery different to others , more appealing,.maybe paint workshops, painting group, snack bar is good..but you are entering food and hygiene, so certain things will be needed..but still doable
as for the actual gallery..location location location… the high street will be to expensive, outer town/village will be to quiet, ….competition…see what is already in the area, …..website, art materials, local painting comps…
it really depends on how much energy you want to put into the business