2. PHP and python are programming languages that are tools, not directions. You can use python to mess with big data, or you can use PHP to mess with big data, it's just that python is more appropriate and efficient than PHP. You can develop websites in python or you can develop them in PHP, it's just that developing the web in PHP is more efficient and cheaper.
So, in terms of direction, web front-end and big data, you can pick one. If you're talking about what tools to use after you pick a direction, then whichever is more efficient and suitable, PHP or python, that's the one to use