Divert a lot of your spending to the 2.5k Capital One card and pay as often as you deem necessary. After about three months of spending in the 3–4k range, you may be good for a 3k increase. Actually, you can check Capital One as soon as you're eligible (six months after your previous increase). If they deny you, there's no clock to reset. And if you receive an offer that you deem to low, you can decline it without penalty.
On the Discover card, request CLIs anytime after the third statement. After that, request 60 days after an approval and 30 days after a denial. There are no clocks to be reset with Discover either. Don't worry about spending. There's little to no correlation between human behavior and CLIs.
On the AMEX card, once you're eligible to request, ask for three times your current limit. At this point, don't worry much about how much you're spending, but do pay in full. Don't worry about asking for too much until you're asking for an increase that takes you over 34k.
