Class C IP's - What are all the things i should look into? Please share your Brain :)

I'm working on a network of almost 20 sites at the moment.
Have 5 Class C IP accounts ( different companies ).

The problem is some companies offer them in blocks like

1.1.1.2
1.1.2.2
1.1.3.2

like that, which means it's quite easy to get trapped by G? ( The class C comes in order like 1 2 3.....).
Also, what about Unique Nameservers for the IP's? Most don't do that.

What precautions & set-ups must be altered here?

Good recommendations on Class C hosting?

Thanks & please share your brain