Creating An Additional Learnable Menu of Spells?

Yes and no, you're going to miss a few things. Catone's patch is probably fine on it own and usable for your purpose. However, Grayshadow's code only add a menu entry in main menu. It doesn't have the logic of the sub-menu coded. If you only want to display the spells / descriptions, you'll need to relocate the C3/20A5 jump table and add an entry for your skill. From there, you'll need an init function, sustain function, cursor positions (you could point to C3/4BE4), list building function (could maybe reuse the dance / blitz code at C3/5623), drawing functions. In short, apply everything the other skills have in bank $C3 except Grayshadow's code, the closest example being Dance. It's kind of a lot of work and a somewhat big first ASM project in my opinion.

As for descriptions, you'll need windhex and the correct table file. The process is easy except if the description is variable length with pointers. I don't really remember what applies here. I think I've seen a thread a while back about expanding spell descriptions.