Hey guys.
We did a project like this when I was in school twenty years ago. 
I suppose that happens when you grow up in cow country.
Check out the MU extension info page - it answers a lot of these questions (how much from what kind of animal, how much fuel produced, design to capture the fuel, etc.) and yeah - I grew up in Missouri, so that’s where I went to school. 
There are legit commercially available small scale digestor setups - that even come with their own natural gas operated generators. I used one in a small commercial grow greenhouse for steam generation and supplemental lighting. Only worked cause we had a pig farm next door which was happy to let us take some of their waste and we could combine that with the leafy material we had ourselves.
Its worth noting that the waste doesn’t just go away - so you still have to handle the composted materials after the fact. And the systems can be kind of “messy”. I remember the first one I made with a big plastic barrel and a 5 gallon barrel - the backsplash and that beast was nasty.
Gotta keep them outside - gotta keep them hot (not just warm, but like summer heat hot) or they are just stupid sluggish. There’s a really cool one next to the Santa Fe dump outside of Kansas City. And most municipalities are collecting gas at their compost sites now and almost all of them are collecting it at their dumps too.
Hope you enjoy your project - generating kilowatts and snuggling in for some crypto mining.