Selection of an e-commerce tool largely depends upon your product range (among other things). As always I suggest to start with the simplest possible tool. Here I am discussing four possible software/tools to build your online store.
(1) If you have a single product you can start your online business with a single page website. This single page describes all product qualities, product images from one or more angles, any testimonials etc. The ‘shopping cart’ in this case will be a simple html form at the end of this page where your customer inputs his/her contact information and clicks the ‘Submit’ button to send the order to you.
By the way, it is always a good idea to start a single product business on side along with your day job. It takes very little time to setup and manage and doable even with hectic day jobs.
(2) If you have more than one but less than 10 products, you can still use the above tools to create your on-line business. Just add more pages. You still get the advantage of doing this with simplicity and without knowing any html/php etc.
(3) Tools mentioned above will become cumbersome to use if you have more than 10 products. Updating price, descriptions, showing onhand qty, calculations of freight, managing inventory, pricing options etc. becomes difficult with simple tools like above.
At this stage you have choice of many tools. I recommend one of the followings:
WordPress custom installation with a plugin WP-ecommerce which may make it easier to build online stores with wordpress. I have not tried this but it does look promising.
Zencart from zen-cart.com. This is a comprehensive and free tool to build your online store. It is powerful enough to manage hundreds or thousands of items with price options and basic inventory management. You can also process credit cards for payment. You can install it on your existing web hosting or you can select a web host who supports zencart. A list of web hosting companies who install zencart with their hosting package is available here. You can also view the existing online business built using zencart.
Initial setup of zencart takes more time, knowledge and effort than wordpress and google sites etc. Once setup, the day to day maintenance is not that difficult.