I also recommend listing a few items first and getting a handle on how everything works before opening up a store.

In saying that, opening a store is a relatively intuitive process, in terms of going through the most basic options and choosing your settings, category names etc, but if you do open one and have trouble with something, it's better to get help for specific problems if/when needed. 

Many sellers use HTML templates for graphics etc in their listings, either designed specifically for them or from a range of templates offered by other sellers / online sites, some of which are free for anyone to use, others need to be purchased. There are a few sites which offer free templates, which you can find in a google search, and they usally have instructions for how to use them. (I personally use FreeForm 2 via Robshelp, which provides a basic 'shell' with fully customisable options so that my template is exactly how I want it to be and relatively unique).