I am spelling and grammar challenged so I am probably not the right person to tell you about writing effective copy. I know first-hand how spelling and grammar errors turn many people off completely. I am told that long text sells better. While this may be true, I believe it's true only after you have developed a lead. I maintain that short concise text attracts more leads in the beginning.
Long text works best to tell the whole story.
Once someone purchases from you once you are in a good position to make more related sales without ANY increased costs. Getting a customer and keeping a customer can be two completely different processes. Its cheaper and easier to sell to your existing customers so don't blow them off by ignoring requests for customer service. Do what it takes to keep them coming back for more. If you are going to make your email address available to your customers, make sure to answer the e-mail that you receive as quickly and as personally as possible.