Appium and Selenium are both different libraries and hence can be used along side each other on a single Macintosh machine, without any issues.
Things you should avoid is mixing your Selenium tests with Appium tests. Keep both of them in separate folders/repositories.
My mac is setup to work with appium with java, but I want to learn appium with python.
Absolutely. Follow the steps given in the installation page - if you've Python installed in your Mac (it should by default I think), then you just need to get a good IDE and grab the Appium Python client and get started.
Has anyone else done this without multiple languages using Appium/Selenium
All I do it maintain separate repos and directory for both of them. The Appium set up is for the app , which is for the web app, which is automated using Protractor