If you could be a bit more specific about where you are switching from and what you would like to achieve/make it would be easier to advise. PW is a very flexible tool with almost all of the building blocks to create great sites fast. I've seen people migrate from typo3, drupal, wordpress etc., so this is all within the realm of possibilities. If you haven't done so already i would just install PW a give it a spin. Play around with some templates, add a couple fields, do some page relations etc.
Regarding your questions:
- Not that i'm aware of. PW doesn't dictate how you setup and structure your sites. It's pretty easy to setup blog functionality though. However, if all you want to do is blog there are other systems available that are more geared towards out of the box.
- Not sure
- You want to use these plugins in the PW backend?
- Haven't tried to input PHP code in fields myself, don't know if this is possible. It doesn't really sound like something you would want to do. In general i think this belongs in template files, modules etc.