lens depends on what focal size you want to capture and what distance, i'm on crop and i do love my 18-150mm for fall colours, you can go wide if its a big scene or zoom into just a few leaves or a single leaf, as for filters, none, i just use the white balance in camera to either correct for the scene i'm looking at or to boost the colours, you could use ND filter if you are shooting a very bright scene and don't want to drop the aperture, a polarizing filter can boost sky colours and take off the glare from wet scenes, some of my vintage M42 mount lenses have nice rich colours to them and the renders are quite artistic in some, try looking at some vintage m42 mount lens videos on youtube, you can get adapters for M42 mount for nearly all mirrorless cameras and dslr
Welcome to the forum.David. There is very little I can add to what Caladina has said. except to actually go out and take some images, then look at them and ask yourself, how can I improve on them. Learning from your mistakes and errors is always the best way in improve your photography.