Mmm... let's see... correct me if I am wrong:
1. For one color: 24/(8! / 4! * 3^4) = 24/136080
For any color: 6 times powered? : 1 - (1 - that above)^6 = 0.00106
3. 4!^6/24! = 3.08 * 10^(-16)... a bit difficult :P
5. 1 / (24! / 4! * 20!)^20 = 1/3.37*10^80 = 2.97 * 10^(-81)