Cooper's Stout Advice

I am ready to start my second batch of homebrew - the first is a hefe in bottles for 5 days now - and I'm debating what to do next.

I have a 3.75 lb can (kit) of Cooper's Stout and 2 lbs of Dark DME from the homebrew store that they sold me with my kit. When I play around with BeerSmith it looks like this will produce a pretty light colored beer, especially for a stout. I've noticed that most extract recipes call for more than 5.75 lbs of extract for a 5 gal batch.

So, I've could:

1- Make it as above: 5.75 lbs extract in a 5 gallon batch
2- Make it in a 4 gallon batch instead
3- Steep 0.5 lb Caravienne and 0.33 lb Carafa III first (I have these from a AHB kit for my next batch and I can just buy some more)
4- Get another can of Cooper's Stout and use both cans in a 5 Gallon batch (what "Homebrewing for Dummies" recommends)

I think I'm overthinking this thing, but I want to give this beer the best chance I can.

You're overthinking it. With 3.75 lb can of Cooper's Stout and 2 lbs of Dark DME from the homebrew store it will be plenty dark enough, and also have that stout-y taste. Plain ol stouts aren't very high in alcohol to begin with, 5.75 lbs of malt extract will work out just fine, IMO. Caravienne and Carafa aren't fermentable malts anyways, so you'll basically be wasting them on this particular batch.