Re: Usernames
You don't use different usernames for addon domains.
When adding an addon domain there is a ftp username which will autopopulate, this is not your username as you know it when it comes to publishing however.
When publishing you leave ALL the details the same as your main site APART from the folder field where you put public_html follwed by the addon domain
e.g. in the main account you just have:
public_html
for the addon site to be published you have:
public_html/tdsproducts.info
etc etc.
That's all there is to it.
Don't aim for success if you want it; just do what you love and believe in, and it will come naturally.