Update: I called Chase yesterday and asked for an increase in my credit limit. Higher credit will look good to other borrowers, and it will help me when I need to make a larger business purchase, and it will make my credit utilization percentage lower. I asked for an extra $10k, bringing my Chase total credit to $25k. I was sure I would not get it. Well, Chase must love me. They must be using some internal scoring formula that is different from the credit scores, because I logged in this morning and saw the credit limit increase!
I also got a targeted email offer for an Amex Delta Gold card, which I will wait for my 30 days to use. I assume that having $25k of credit with Chase in good standing is going to do a lot to help me get other credit. I'll update this thread a month from now.