If I were you I would firstly revamp the entire site onto Wordpress and add this with Magneto for the E-commerce side of things. Not only will this make the site easier to use from the back-end, Wordpress also has a huge community, plugins, themes that you can use to your advantage.
As for the theme I would invest in a $30-$40 responsive theme from themeforest. I would also highly recommended that you get on that is minimal and bright as this makes it easier to navigate for end users.
Get a brand on the go something sticky that people will remember and then keep your site within the same colour scheme. Usually something like the whole site being white with black/grey text and then stick with one secondary colour for all the other little extra bits. Be consistent.
SEO. Optimise the site to the limit and then some more. With Wordpress I would recommend Yoasts all in one SEO plugin, this provides in-depth optimisation right down to the details.
You also want customers to be directed to the money maker. At the moment the homepage looks like and about us page. Make a compelling call-to-action as soon as people hit the site. Make sure that people know where to go next straight away. Things like special offers and so on always increase the chances of this if executed correctly.
Look up your competitors and get some ideas. This is always a good way to improve sites, you never know you might see something they do and say 'I can make that even better'.
And lastly, if you do decide to go with Wordpress here are some extra plugins to further improve the site:
W3cache (to speed the site up)
WP Super Cache (same as the above but only use one of these plugins)
Marketpress (for e-commerce)
BackWPup (for backing the site up)
Fancy Excerpt (does what it says on the tin)
Microkid's Related Posts (if you do decide to add a blog this is always handy)
Scroll Triggered Box (get people on a
newsletter for potential future deals too)