I have also been a Auctiva Commerce user and I agree VEHEMENTLY with dwm here - don't go there - u will be starting out with a BAD impression of what online marketing and ecommerce can actually be like. It is just an extra headache you do not need. Things are challenging enough without that kind of stress.
Although ecrater does not give you full control of your ecommerce platform, it is a good place to start if you are working with limited funds because it will help you to understand the business without you having to fork out tons of money in the learning curve, since setting up there is free.
Once you have had some experience and understand your market better, then you can look at other options which will offer you more full control of your ecommerce platform, and still keep your ecrater site. Since it's free, you have nothing to lose except your time which you would have to spend no matter where you go.
my 1-1/2 cents worth.
P.S If you have a little bit to invest in the learning curve, I could steer you to a great program that is well worth its cost. PM me, if you are interested.
Either way, all the best in your new venture. Above all, don't give up! Peace!