I can answer the first question for ya, yes you can use html (and any of the extensions) on as many sites as you want. You have a developers license when you purchase, I read it somewhere on the site.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.