dpd1 - 9:11 pm on Oct 14, 2013 (gmt 0)
If the special theme is unique and especially timely, then it might work. However, I think for that kind of stuff to work best, you have to keep on coming out with unique things that take advantage of currents trends and events. But yes, a lot of people do that kind of thing, so it might be rough.
As to all the other stuff... I'm not a tech wizard when it comes to the actual site stuff, but I do believe that the more you can do yourself, and the more centralized the experience for a shopper can be, the better off you are. I run into other site owners that literally do nothing themselves, and I honestly don't know how they make any money. By the time you pay off everybody else, I'm surprised there's any money left at all.
As has been suggested with start-ups like this before... Start small. Learn to build your own site. Start with PayPal. Learn to get out there and pound the virtual pavement, getting the word out in the right places. Don't just rely on SEO, put in the manual work. Put more into the site than just making it a cookie cutter sales site. Give people more reason to come there than just that. Test the waters that way and see what happens. Taking the... 'If I build it they will come' approach, and throwing a bunch of money at it, is no guarantee to success. In fact, you may very well be quite disappointed.