5-6 panda cories would be ideal. Make sure you have a sand substrate, though, as they have such delicate little barbels.
I'm going to disagree that it's bad to add both - as long as the shrimp have hiding places (to hide from the betta, the cories will ignore them) then it is perfectly fine. Shrimp contribute very little to the bioload, won't bother the cories, and don't actually need that much care, just relatively low nitrates. I have about 50 cherry shrimp with my cories and sorority and have never encountered any problems.