Hi Luke,
Thank you for your question 
The MetaGrid Pro version of Dorico is a demo one although it works, did you find it?
If you only have MetaGrid (not the Pro version) it might not be there.
[MGP version: Content manager > Grids > Presets]
You would have to add more buttons to customize to what you need. The MGP team are currently working on a new beta of MGP and a Mac version which will make creating grids, buttons, key commands etc. much easier to set up. (These kinds of tools are very tedious to set up as you probably know.)
I am not part of the beta team but they say it should be coming out soon (nothing said about a Windows version).
Also since you already have a Workspace/Grids, you could try duplicating a few of your Finale grids, reprogramming them for Dorico and see what happens.
[Aside: as Dorico works in different ways, what you come up with might not be the best way of working but at least it is a way to start. If it were me, I would look at some simple tasks you are doing, and replicate that on the buttons from a duplicated Dorico equivalent grid and trial it.]
As I pointed out in my initial post, for my current divisi (etc.) tasks, making the same layouts for each program helped, but normally for Sibelius I have a different layout than my Dorico one. Actually for Dorico, I use the built in key commands within Dorico most of the time (and the Jump command!) I made a start with adding in the Keyboard add-on (MGP version) for note input, but I decided to wait for the Mac version to be released before continuing with developing it.
The Stream Deck Notation Express (Dorico) would have many of the buttons already mapping, so all you would have to do (!) is customize the layouts (grids) for what you want where and on which layout (or just use it as it is for a test.)
Here is Notation Express layout information from their manual just to give you an idea of how it is organized and what is included
Notation Express XL version
A sample page from their manual, Dorico filters
I like Stream Deck because it has a positive button action I can feel (unfortunately accompanied by a “plastic button sound” as you use them, annoying anyone in the room wanting quiet.) They are not too noisy, but you hear them.
I see on their website a 60 day easy return currently, but you might be able to purchase it locally if you also get a return option.
I have had problems with MetaGrid Pro, connection problems, sometimes buttons work intermittently (some Sibelius actions would either work or have an unpredictable result, whereas setting up Stream Deck with the same key commands worked with no problems.) And MGP would often crash, especially when creating buttons. But it’s obviously working for you very well
Icons
MGP has hundreds icons to choose from, all built in.
Stream Deck has very few, so often I just use text, and maybe a basic color or use their website editor to create something basic, unless it is really annoying me and I have some time to make one.
I hope this helps,
EDIT: I am not sure if Stream Deck has a “Momentary button” function, never needed it, but I was just setting up one in MGP just now. I seem to remember some functions are not available on the other but never wrote a list of them.