Glad to see it working 
The two most common archetypes I seen in an ytyp are :
- CBaseArchetypeDef = Prop definitions
- CMloArchetypeDef = Interior définitions
bbMin / bbMax = Boundig box min / max (in short, the ‘extents’ of the prop)
The GUID must be unique in the current file otherwise your props will disappear.
Manifests just need to be placed in /stream folder. And yes they can be used to create ymap / ytyp relationship.
The ytyp is not necessarily loaded by an ymap, it can be loaded directly as an DLC_ITYP_REQUEST (what we do the easy way with FiveM __resource.lua data_file entry).
In your case it is loaded by an ymap, thats why we proceed that way.
There is plenty of tiny details but your assumptions are correct.