I recently started modding myself and have learned a lot just by browsing around the forums.
I recommend you start by taking a look into the game structure (by changing the “.smod” files into “rar” as stated above), especially the Entities folder where you’ll find the items, structures, furniture, etc…
But basically, simple things like objects are folders with a couple of items, usually a definition (.json) and the graphical file (.qb), stuff placed in the world (like furniture) also usually have iconic forms (Another .qb) and two extra definitions files for their iconic form and their ghost/placement form.
After that, I recommend you take a look at SHED, the modding software included with the unstable release of the game. Just navigate to the game folder and look for the SHED folder.
From there you can create a new mod and “clone” (by right clicking) entities, like… you could clone a piece of armor or clone a workbench to create your own clothes or workbench from the ones you cloned to your new mod; the software also handles updates to the Manifest (the important .json file which is the definition of your mod + your aliases (entities and such), mixins, etc…) so with shed and a bit of patience you can have a simple mod (like adding a piece of furniture) up and running in a few minutes!
I’ve found (personal experience) that the best way to learn how to mod stonehearth is to just delve into the game’s content itself since it is basically a big mod. Stonehearth IS a mod, the base mod, and by “copying” and editing from it you can learn a lot.
As for exporting from Qubicle, go to export, choose .qb and then untick “compression” and change the dropdown axis to “Right-handed”; if the “individual export” is tickable, that means you’re dealing with a model of many matrixes (like armor pieces) and you should always export it whole, not individually!
I know it’s mostly sparse but I’m still getting into it myself, just sharing some noob experiences too Hope it helps!
Oh, by the way! Forgot another thing I did that HELPED me a lot!
I looked for similar mods (that added the same kind of thing, etc…) and downloaded them - and started browsing their files. I learned several important things from these, especially how to work with mixins!