I don't have much experience with microworms, so can't help you there. I tried them once, but they are so small, I did not have the patients to dig them out of the soil for feeding.
I do feed black worms. I don't have a local seller, so I get mine here Aquatic Foods Home Page
There is a care guide for black worms on this site. Since I mail order, I have to buy 1lb at a time. If you have any fish keeping friends, maybe you can split the cost. Most all of my fish, love black worms. These worms will parish over time in the fridge. If rinsed often, I have had them keep over a month.