It is common for very young buns to have somewhat moist poop. As you are saying, young buns should get nutritious food like alfalfa hay and pellets, to ensure normal growth and development. This means there will be a certain surplus of nutrients, and that surplus gets pooped and peed out. It’s not sth to worry about as long as the poop isnt consistently runny or full of mucus.

A sexually mature rabbit will produce big, somewhat shiny territorial poops. They’re not sticky or moist, they’re  just big and, to a bun owner, beautiful. They really do smell like cooked onions 🤣 The territorial poops  tell other rabbits that the territory already belongs to another rabbit.

I dont think your bun’s moist poop is cause for alarm. If he is eating, pooping, peeing and being energetic (not energetic all the time, baby buns sleep a lot), I think this will right itself with time. It’s good that you’re mixing his alfalfa up with timothy (or other grass hay), because grass hay is the most important food for the  adult bun. Your bun should be weaned off alfalfa at around 7 months of age.