Such a cute themed puzzle, and I think 4A, 5A, 1D, and 2D nail the format. You found really nice breaks for things like [Element at 18] and [Down to disobey]. 1A's a stretch, but I'd allow it for the sake of the theme (I don't think I've ever seen an acrostic translate a number like that before. 3D is the only one I'm perhaps not getting; it's H+ONE+D but as an &lit, is it also actually cross-referencing as Primarily happening exact? That doesn't seem quite right, but maybe I'm just misparsing!
I think your parse is right, but I wouldn’t call it a semi&lit — typically in a semi&lit the whole clue is the definition and a subset is wordplay, this has the reverse going on.
Really fun idea and very well executed, a lovely puzzle! Giving me all sorts of ideas for clues that would be wildly unfair out of context: [Forefathers of 10A going mad (9)]