21" Razr's or 21" Holeshots

[Team Outlaw #34]

I have some questions about some tires:

Ok i want to get 21" front tires so i can use my 20" and 18" rear tires....

I was wondering if 21" front tires and my 18" tamers would be a bad setup for motocross?

I was wondering if the Razr 20"x6" tires have the softer compound?

thanks for the info