1. Your positioned for the Art market but your site looks so corporate. Have a look at the design for smugmug.com (targets photographers) and carbonmade.com (targets artists).
I'm guessing your market may assume that your a fly-by-night operator who bought a template from somewhere and isnt really serious about the market.
This is just my opinion - you can easily A/B test this with another design.
2. There is no testimonial on your homepage. This is not good.
3. You can only figure this out if you start A/B testing. There are a lot of products out there which will let you run experiments without changing your homepage. So start doing that.
http://blog.kissmetrics.com/landing-page-design-infographic/
4. I should be able to build the site first before logging in.