Compost King
Free Ranging
The only Mulch I see as bad is Cedar, there may be other woods that are bad but I am not aware of it. I say use the mulch, it might be the perfect bedding for a run. Mulch also increases bug procreation. Absorbs odors well too. I have been making my own mulch a little bit everyday with a pick and rotted log.
How you do the floor is up to you. I like a lot of air exposure to the bottom of my bedding, and in those rare cases where I keep water in a coop I like to have something that lets the water flow down and dry out. if you leave gaps in the wood its best to leave tight ones so bedding doesn't fall out of it like what happened to me. If that does happen I showed the cardboard trick to prevent it. I only posted that to show what I do with a pallet floor and the issues that comes when you make it too loose. No big issue to me but others might not like going out on the cold morning to install cardboard.
How you do the floor is up to you. I like a lot of air exposure to the bottom of my bedding, and in those rare cases where I keep water in a coop I like to have something that lets the water flow down and dry out. if you leave gaps in the wood its best to leave tight ones so bedding doesn't fall out of it like what happened to me. If that does happen I showed the cardboard trick to prevent it. I only posted that to show what I do with a pallet floor and the issues that comes when you make it too loose. No big issue to me but others might not like going out on the cold morning to install cardboard.