Further notes for Tabletop Simulator:
Assets from Older Libraries that are Broken
You'll likely find many workshops that were made several years ago, and may have broken links to online libraries or repositories that got moved or deleted in the interim. You can identify these in-game by a white floating "marble" (denoting a lost 3D model) or weird textures (denoting the surface graphic has been lost).
The "Counting's D&D" workshop has a few such missing assets, most troublingly the dungeon walls.
In order to get some good walls, as well as trees, boulders, interior furniture, and plenty of other great freely-made items, I found a good
collection on Steam of assets.
These also are missing several models and textures, but as of two nights ago there were enough to build a very nice library. If you collect the specific items you like, and then put them into a "Bag" (Objects > Components > Tools > Bag), you can then right click on the bag itself, rename it descriptively, and then Save Object locally.
The items inside the bag should now be backed up on your own computer, so you can use them even if the online repository gets delinked or broken.
Setting Fog of War and Line of Sight
You can create a fog of war by clicking on the F3 "Zone" button, and selecting Fog of War (second from right). This allows you to create an intangible cubic volume where stuff inside is invisible (except for whoever is "Player Black" in color, i.e. the GM).
You can manipulate, resize, rotate, and raise-lower-move-around this FoW just as you can any other 3D object in game. If portions of your map are invisible at start, you can cover them with FoW (e.g. the interior of a fortress).
To give your players Line of Sight, you'll need to generate a figurine for them. For a 2D figurine (like a boardgame "standee") go to Objects > Components > Figurines > Custom, then left click to place on the board. Hit Esc to stop placing.
For each standee, you can import and upload a graphic. So if you have a good picture of Marge the Barbarian rippling her unibrow knowingly, you can Browse Local Files and select the local .png or other graphic, and import it. Make sure to click "Cloud" and "Upload" otherwise other players won't be able to see it. Once the upload is done, click Import and the miniature should be illustrated.
For a 3D figurine, such as a .unity3d model from HeroForge, click on Objects > Components > Custom > AssetBundle and left click, then press Esc. As above, Browse Local Files to find the relevant model you want, and click Cloud and Upload. Once the Upload is done, press Import and the model will appear.
Once a player has a model, right click on the model and select Toggle, then select "Auto Raise" so it's off. This means the model will no longer automatically teleport upward in the Y-axis so as to surmount any and all given obstacles, instead being properly blocked by walls.
Then right click Toggle again, and select "Reveal Fog of War". This means the figurine will reveal objects as it passes close to them in the FoW.
(Query: how to set variables for the distance of reveal?)