In the world of polishing, pretty much anything combined in the main ingredient of elbow grease works. No magic here. As crusty as you started with , some 80 grit work was in order.
All a matter of on hand stuff & preferences, you can sand finer & finer till just a rag buff & liquid compound can complete it, or stop sanding sooner & power into the surface with coarser buffing products , such as a large buffing wheel on low speed grinder & stick compounds. Metal buffing wheels & compounds offer the largest variety of abrasiveness & the most professional speed. Most equipment investment cost. Time spent will vary with any methods, but final result is mostly all that matters here for a single project.
Most polishing compounds are made from the same stuff as the bar sticks for buffing wheels. For general cleanup & maintenance, I'm starting to prefer the green types of liquid polishes over white or grey. Mothers billet will give the finest final finish over a really smooth clean part, but is waste of time otherwise.
I think sharkhide is the rename of another similar product (ZOOPS??) & is known to hold out for a decent time period. Haven't used yet, but worth a shot.
Protection from any wax or polish will be minimal lasting time, end of story. Facing harsh use, even aluma-lube or wd-40 would be short term better than nothing . Just to mention for the underside of a truck used harshly, spraying with diesel was an old farmers trick, particularly for a new truck. body crevises & all.
With an aluminum product fully polished to perfection, ceracote mc160 clearcoat is the only clearcoating I know of for skilled diy use proven to stick & hold out indefinitely. Gun people like it , so you know it's tuff. It is an air dry product, single part, that can be sprayed with small sprayer. Haven't personally bought & used yet, but familiar with it's solvent, which is tert butyl acetate. Used in conversion varnish, which is super durable interior wood stuff. Strong stuff, need good mask. Any clear will be a little duller than perfect polished aluminum, but is the best permanent final solution to constant maintenance I know of.