1)is there
a difference between the 2 ways I would wire the dvc subs?

No, your amp will push the same RMS and each VC will get getting the
same RMS either way. 1)is there

2) if I
went with the single vc subs, would there be enough of a difference
between the sound with 600RMS with the cheaper amp VS getting the
total load to be 4 ohms and having to pay more for the more powerful
amp?

I dont know the answer to this, but DVC subs are typically higher-end
than single VC's ones.. I know 4 subs running 150RMS each will be
louder than 2 subs running 300 ea, but I doubt that applies to VC's,
since they'd be moving the same cone. I'd think that the DVC's sound
better.

FWIW, I swapped out my SVC subs for DVC ones, and they sound a million
times better on the same amp.. Of course you gotta factor in the
difference between MTX's (hi-end 10 years ago) subs and brand new JL
12w6v2's, so it's probably a useless comparison...