You NEED a filter, no questions asked. It's what starts the cycle, it's where the colony begins. If there's no filter, then the cycling process won't even start at all. Let me quote "You NEED a filter, no questions asked.". There's no but or if, it's just the way things are. (;
As Hallyx as said, doing 100% changes will kill off the BB that we need. It's everywhere in the tank. Decorations, water, and especially in the media. You can do 80% changes but don't take out all the water. OFL does recommend 2 50% changes per week. 1 with vacuuming and 1 just with water.
Just do 2 50% changes per week for 4-6 weeks and you're good to go. Get a liquid test kit, preferably API. If any ammonia shows up, then do a water change. But DON'T do it everyday. This will stress the fish and will bring down their immune response.
I don't recommend Prime in the cycling process as this will give false readings if ammonia. Even if it may be possible to injure your fish, you still don't want that to happen.
Co2 is not needed for all plants. I presume filters don't produce Co2, just gas exchange. Easy and hardy plants such as Java Moss and Duckweed don't really need anything at all so you don't need to worry about that.