Do I need to download any software?
No you can manage your site entirely through a web browser
Do I have to know HTML?
No you do not need to know HTML at all to manage your website!
Is there a limit to the number of additional pages I can add?
No there is no limit to the number of extra webpages you can add to your website.
What software do I use to manage my website?
You use the online dashboard at http://www.myweblogin.com