Cap 1 definitely has credit limit "tiers" tied to many of their cards (and annual fees sometimes), and your credit when applying determines what you get. The prime cards, like Venture, shouldn't be that way, but who knows with them. They are very good for what they offer, but definitely fall far behind many other prime lenders once you're into 5+ figure credit limits. Venture looks to be a step in the right direction. At one time, their Platinum Prestige card had a max $30k CL, but most were $20k max, and several were $3k and even $500. This was prior to the credit meltdown. Times has changed, as we know. 
As far as combining cards, they were very accomodating of that prior to the credit meltdown, then they stopped allowing cards to be combined somewhere around 2008-09. I don't know if that's still the policy or not.