It's perfectly safe to use different brands, as long as skin care is for your skin type, and makeup is non-comedogenic. Yesterday, I wore eyebrow makeup from Clinique, mascara from Lancome, eyeliner from Cover Girl, blush from Maybelline, and lipstic...
You should write to Chanel for clearance to do so, you don't want to be sued if they find out. Since the jewelry looks exaclty like Chanel, it is trademark infringement. You will be sued.
I wouldn't use any concealer under a fake tan as your fake tan will just wipe it off. Put your fake tan on, let it dry, then dab this concealer on the marks on your arm. I'm a makeup artist and have tried almost every brand of makeup and this is by f...