Let me help you a little bit to make things SOOO much easier.
First, while you can use myphpadmin, I would not advise this if you are going to spend any time in the database. Download from mysql their Mysql Query browser. However, keep in mind that the only way to use a tool outside of myphpadmin is to have a dedicated IP address for your domain.
Now, as far as testing server. It's advisable for sure, however what you can do for the sake of testing is create a subdirectly on your domain and use that as the testing environment. That way you don't need to load php, mysql etc. on your local machine. It can be difficult & easy depending on your configuration.
Anyway, I hope this helps. You will find (once you get your head our the eCart and PowerStore) that Webassist really does improve our lives for churning out ecommerce websites.
I built several of these sites for Nike using Webassist and they really deliver.
Best of Luck,