Looks like you're doing well with what you have, but you may be out of luck re: anything Walmart unless their own card offers more or you use one of the 2% on everything cards like Fidelity, since Walmart and Target are often specifically excluded from rewards schemes (as you note re: Citi Custom Cash, which I also use for 5% on groceries).
Of course, for Target, their own card gives 5% so that's what I use.
I had been using my CapOne Savor (3% on groceries) before I got the Citi, and it still offers $200 bonus for $500 spend in 3 months by referral if that's useful. I still use it for dining (3%), except right now Discover is 5% on dining this quarter.
You may have the 5% offer to activate for gas on the Chase Freedom, though.
OMG, it is so nuts to keep up with all these things, LOL. I maintain a note on my phone to remind me of which card to use for what when. Ohhhh boy.