Amiga OS resident modules (libraries, devices, etc...) are location-agnostic, in that it is technically possible to compile them as location-independent code to be loaded at runtime from disk, or to compile them with fixed addresses to be stored in ROM, and Exec will automatically fetch and activate them in both cases. For example, for libraries, probably the most known example of this characteristic is the
workbench.library in the A4000T version of the 3.1 Kickstart ROM, that was moved to disk due to space constraints.
Additionally, filesystems can too be stored on disk in the Rigid Disk Block structure on hard drives, and the system will load and link them at boot.
Now, suppose one wants to assemble a custom Kickstart for Amiga that can boot right into a regular Workbench, while keeping the modules in ROM to the bare minimum needed.
What is the minimum set of modules that are strictly necessary for the Amiga to boot into Workbench and can't be placed on disk, under the assumption that you do not want to modify the modules?
What would be the minimum set if one was to eventually provide a bare-bones implementation of a graphic toolkit to assist the system during the boot (mainly for diagnostics), that is until the system passes the critical state that allows it to load the full UI subsystem from disk?
Addition: as correctly pointed out, A1000 and early A3000 can load a Kickstart from disk, however the question here is a bit different: which libraries, devices are absolutely needed in the Kickstart for the machine to bootstrap the system. Especially after Kickstart 2.0, when the Kickstart got in it many modules that arguably are not "core" and could have lived on disk (think about Gadtools....).