Can someone take me through the rules with heads and amps, I'm looking at getting two separately possibly.

Do they need to be exactly the same type, just the same brand or is it anything goes?
First off read the FAQ section 5 and 6. There is some excellent info there for matching heads and cabs. Read that and you will know more than some of the people who allegedly work at my local GC (there's a long horrible story there which I am not going to go into here).

After reading that...come on back and post anything you didn't find covered. And no, they don't have to be the same brand. I am not sure what you mean by type.
Just make sure that the cabinet has the same or a higher impedance rating than the head (i.e. use a 4 ohm head to run an 8 ohm cab..or two 8 ohm cabs (total ohm load of 4 ohm). And always use speaker cable to connect the head and cab! Instrument cable is a no-no.
Cabinet mixing is where it's at. But, like said above, make sure the impedences match, and that your head can handle impedences.
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