+1 to keep the Atoma for flattening as it doesn't last as long as a coarse stone when used for metal and it's more expensive to replace. It's a great tool for flattening, though, and the plate itself is a useful reference for flatness and straightness. I'd recommend using "good" stones like your Naniwas for medium (c. 1k) and above, when you have the profile and geometry sorted and decent bevels that are relatively chip-free, plus a "good" 300-500 grit stone for "good" knives that are bought new or are well-maintained, and comparatively less expensive coarse (<320) stones such as the "pink brick" for heavy chip removal, reprofiling, major thinning, and similar rough work. Coarse automotive sandpaper is also a good option (as is Benuser's advice in general).
I also use a Sigma Power Select II 240 for work that might be better suited for a belt grinder; it is a useful tool for my requirements (very fast, portable, for repairing knives in need of significant metal removal) but gets used up quickly and requires frequent flattening while being more expensive per unit of work accomplished than slower options. I consider that one to be a special purpose, niche type tool as opposed to something generally recommended for everyone, but depending on your plan it may be worth investigating -- I believe they also make a 120 in that line, but I don't know how well it would work going from that to a 1000-range stone.