Do NOT link directly to WA but as you are directing to your own site you should be OK. However perhaps the landing page should be very informational before you get to the sign up. I have had my adwords account suspended even though I have not run any ads for a year. They say that they did not like my landing pages.

Are you promoting WA with Google Adwords? I read in the forum some members had their accounts closed by Google when doing this - I also remember a post by Kyle agreeing Google adwords may not be the best place to advertise WA. I'd be very interested to hear how you get on. I may be wrong but you might want to check with Kyle. It could save you some time and money :)