Does MAMP installation create conflicts with standalone MySql?
I wouldn't anticipate any problems.  I've seen those configurations work just fine.  The only concern I see is that the built in versions of the software get updated automatically by Apple, and the versions you installed will not.  However, Apples updates include the latest fixes more slowly, so if you are diligent in installing them, yours will be up to date a little sooner.  If you are not, the Apple versions are easier to keep updated as the updates are almost completely automatic.