Ania, you are right on...
Top Producer is a preferred vendor for KW. Top Producer has an option for KW agents. It does the touches from Gary K. automatically for you!!!!!
All you have to do is set the specific action plan that you want to a prospect email address and Top Producer will automatically send emails for you to your prospect and remind you when you have to call that prospect. The Keller Williams option in Top Producer is exactly what you are looking for if you are serious about following Gary's approach.
I pay about $130/month but as Hugo mentioned, they have a larger product base and I use most of them (Top Producer 8i, Top Producer website, Market Snapshot, Top Connector...).
The basic Top Producer 8i is the web application you need. Not sure about the price for this only, may be around $30 (check on their site).
Hugo is right; Outlook is great as mail software but is not designed for the real estate industry. It might be much cheaper but is not an option for your business needs anyway