Any combination is fine, I like to give ideas rather than recipes.
The main principle is how it’s easier to sow and plant into fine compost, so keep that for the surface layer. It may be old animal manure. Any kind of manure is possible, often they have different qualities, also arising from the bedding used.
Mixing is an option of you want to, it’s just less work not to, and worms etc do it in the end.
