How to transition from PHP to Python Django?
No. You can only do a LOT better.
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No. You can just change 'mysql' to 'postgresql' or 'sqlite' in your settings.py.
NO! Python would never give you the right to mix up everything in one file and make the shittest shit in the world. Templates, static server.

Django is a Model-Template-View framework, great for any applications, from small to huge. PHP works fine only with small apps. Yeah, PHP == Personal Home Page, lol.
P.S. Also you can minify your CSS and JS. And compile to one single file (one js, one css). All with django-assets. And yeah, there's a lot more reusable Django apps (for registration, twi/facebook/openid auth, oembed, other stuff). Just search Bitbucket and Github for "django". No need to reinvent a bicycle, like you do with PHP.
Here's my background:
Decent experience with PHP/MySql. 
Beginner's experience with OOP

Why I want to learn Python Django?
I gave in, based on many searches on SO and reading over some of the answers, Python is a great, clean, and structured language to learn. And with the framework Django, it's easier to write codes that are shorter than with PHP
Questions

Can i do everything in Django as in PHP? 
Is Django a "big" hit in web development as PHP? I know Python is a
great general-purpose language but I'm
focused on web development and would
like to know how Django ranks in terms
of web development.
With PHP, PHP and Mysql are VERY closely related, is there a close relation between Django and Mysql? 
In PHP, you can easily switch between HTML, CSS, PHP all in one script. Does Python offer this type of ease between other languages? Or how do I incorporate HTML, CSS, javascript along with Python?