I'm noticing there is lots of ServiceNow provided information about features and technical history (which makes sense):

I haven't yet found a "checklist" of work that we will need to undertake to make the move. (it might be there still looking).

I see we will need to configure Landing pages and guided tours.
I understand this can essentially pre-load these pages with "favourite" that a new user would not normally have with ui16.  It could help them be more productive at the start. 

I'm seeing how we could use Guided tours as an alternate tool for training.   This might satisfy a desire our users have expressed for more interactive training.  (while we may not have the energy for training environments, test data, exercises and evaluation... We probably have the time to provide guided tours that FEEL more like they are "in the tool" not "about the tool".)

Workspace Selection
With 50+ workspaces available from ServiceNow (as of Washington) we'll need to understand which workspaces work with our licensing (and the modules we are using) (not using HR etc.)  And we'll need to select/request the configuration of those workspaces to be available in the unified menu.

Theming Choice
I see that there is lots of ServiceNow content about themes and at the same time the ServiceNow recommendation is to use Polaris because it has been well tested and has a dark mode. So we'll most likely follow that advice.