These are excellent points, especially about validation.

Question to OP - Why not have a freemium model - where if the user does not pay then his account is downgraded to free plan. This generally has the benefit of keeping those users interested who may pay for the service sometime in the future.

As an example - I used Zopim on my website for a whole year for Free before converting to a Paid user. Had Zopim not had a free plan, I would have tried other competitors and eventually become a paid customer of theirs. By keeping a free plan, they retained me as a customer.