We understand that there is not a big market of individuals who know Shopify. We want someone who is absolutely proficient with slicing psd files into awesome, clean xhtml and css. Learning Shopify's Liquid language will come over time. It's rather simple so if you are a mid-level PHP person you'll do fine. Extra benefit for us to have someone take Shopify to the next level in learning their API.
Regarding other projects... we do a lot of WordPress projects. Having a strong background here will help and fit nicely. We also are moving away from Magento self hosted versions to Magento's GO solution. A hosted platform provided by them. So if you are familiar with Magento's design process that would be great as will will still continue to use this software but without getting into Core edits.
We use Basecamp for project management, and freshbooks for timetracking on projects and invoicing.