Basic modding info for a noob on rooted Xperia Z3 ...

Hi people. I am new to this game. I have rooted xperia z3 (kitkat 4.4.4), locked bootloader, cwm/twrp/philz installed, T/A partition backed up.
I am going to ask a series of questions and hope that someone has the patience to answer (some of) them. I'm trying to get an overview of what is possible and what is dangerous.
1)Can I flash stock firmware without unlocking bootloader? Or does flashing always need unlocked BL?
2)Is there a way to update to Lollipop without losing root?
3)If I unlock BL and flash a custom rom can I then reinstall apps and data backed up with Titanium?
4)What happens if I restore my T/A partition whilst running custom rom. Will camera function be restored/improved?
5)If I'm running a custom rom can I enter recovery on startup in the usual way and reinstall a backed-up image of stock rom and data (nandroid??) in the usual way?
6)If the answer to 5) is 'yes', when do I restore T/A partition?
7)If the answer to 5) is 'no', how do I get back to rooted stock rom, locked BL and DRM keys intact?
8)Should I just forget about all that and install Xposed...?

I hope it's ok to ask that lot. I wait with bated breath and thanks in advance...