[Help] New to the Flashlights world, looking for a good tactical one.

I think I need some answers before choosing a flashlight.

  1. Batteries - I have these (2 of each) Dropbox - Error - Simplify your life
    Can I use them? They don’t have both sides flat… (can I remove the bump some how?)
    Also, can I use 2 cr123 batteries instead? Which configuration is better?
    Btw, someone just told me I can get cra123a batteries for free at the radio department anytime,
    so that can help with saving money.
    And if flashlight supports cra123a batteries or 16340 does it mean it supports the other one as well?

2. Light color - any major difference between 6000K-8300K? Which shade is better for me?

3. Can this chrager charge protected batteries?
http://www.fasttech.com/product/1137904-miller-ml-102-universal-usb-smart-charger-version
Can it charge 18650 batteries with a “bump”?

4. I’ve been searching around for information and found this topic - Cree, Luminus, Seoul Semiconductor, and Nichia LED comparison
Can I just assume that the one that generating most lumens at, let’s say, 300mA, is the brightest one?
So if the led and the battery are determinate the lumens, how does the host matter?
Is hosts are just for zooming, different glass in the front and heat management?
I think I’m missing something important… :~

5. So let’s say I bought this flashlight -
http://www.fasttech.com/products/1601/10000911/1626602-ultrafire-wf-501b-1-cree-xm-l2-t6-1-mode-900lm
It says 900 lumens at 2.5Ah. Can any battery run at 2.5Ah?
Or do I need a specific battery that can?