Rarely do I say to talk to a coach, but here's a great opportunity where a few minutes with an expert will help you a lot.

Open source shopping carts are great -- however, there are always hidden fees. If you have a full time developer then by all means - open source is fine. However, if you do not want to worry about that part of your business, think about it economically. While you sleep, Shopify is fixing bugs and running servers all for $30/month or whatever. $30/month multiplied by 12 months? Can you get a full-time developer who will work 24/7 and pay for your hosting and merchant services for less than that?

Cheers -