I'm afraid you have gone down the wrong path. You shouldn't modify the mojoPortal code or DB tables to achieve what your various requirements. The reason is that you end up with a forked version of mojoPortal and you will not be able to easily upgrade. I highly recommend that you revert any changes you made to any mojoPortal code and DB tables.
That said, now that you have figured out how to add fields to the Register.aspx, using the mojoProfile.config, you can programmatically access those added fields. They are stored in the DB, but the easiest and safest way to access their values is use Helper Methods implemented in mojoPortal. At the very bottom of the User Profile Configuration (http://www.mojoportal.com/userprofileconfiguration.aspx) document, there is a section that states how to do this.