I would used manure that has been mixed with carbon-rich material (like straw for example) and then allowed to hot compost for a bit (maybe a couple of weeks if well-controlled, longer if just sitting in big outdoor heap). Cow manure likely has all the nutrients the worms need, but on its own (especially fresh) it can cause harm (ammonia release, salts etc).

Sarah – unfortunately my goto response of “it depends” definitely applies here. My preference is to let worms grow into a particular system rather than trying to maximize things right out of the gates. You’ll have a far greater chance of success. In other words, I’d suggest starting with FAR more material than worms – and make sure the initially habitat material is very well aged (I’d even test a small amount in a separate system to be safe).
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Barbara – I’m guessing you mean “maggots”. If your system is outside – especially if you happen to live in a warmer region – these are likely Black Soldier Fly larvae. They thrive in composting systems. My recommendation would be to add less food and more bedding to help out the worms. But in these outdoor systems it can be pretty tough to avoid some of these other larvae altogether. The good news is that as long as you are meeting the requirements of the worms (in terms of temperatures, moisture etc) these other critters shouldn’t cause any problems.