Michael - it sounds like the very first thing you should be doing is setting up a copy of Moodle on your local computer. That way, you can turn on debugging to 'developer' level (which you don't want to do on a production site) and you can directly edit the files in your plugin, without having to upload them every time.
You also have the option of installing xdebug and being able to set breakpoints and step through your code a line at a time.