Build Wordpress Website with Membership Facility & Database Functionality.

I need a website building using wordpress to replace my existing website which is built with Joomla.

I want the new website built in wordpress so that i can take control of updating content (which is difficult with the Joomla interface), better SEO but also to allow for advanced internet marketing strategies.

I have a liscence for a wordpress theme called Optimize Press which is used mainly by internet marketers in building "squeeze" & "landing" pages but it also can be used for membership sites, I am hoping that this theme can be used for the project.

My business is installation, servicing/upgrading security systems and aswell as having the usual; Home, About, Contact pages etc...the idea is to create a membership site so that my customers can login at any time with a username/password and update keyholder details (up to 4) in the form of names and telephone numbers.
To explain this further: My customers have intruder/burglar alarm systems that if activated when they are away can sometimes be a nuisance to neighbours. The free registration membership section of the site must allow a user to login and register, their best email address and up to 4 names & telephone numbers of keyholders to their home, so that we can access the database and contact the keyholders if we are informed by a neighbour that their alarm system is ringing (our freephone number is visible on the alarm box fitted to the outside of their home). So it's basically a "Keyholder Registration Service".

The reasons that I would like to use Optimize Press for the job are:
I already own a multi use copy and don't want to pay for another theme.
I want to ideally use this one theme for not only this but for other web projects.
It comes highly recommended by an internet marketer who I am working closely with.
It is designed for membership site use.

Here is a link to the optimize press information page: http://www.optimizepress.com
I do have a support login if we need to ask any technical functionality questions.

Thanks...