Yes. Well, CC2 files actually, but they are fully compatible with CC3.

Since what you are looking for are essentially just simple markers, if you don't find what you are looking for elsewhere, you can easily just draw them yourself and define them as a symbol. See page 75 of the user manaul that shows step by step how to make a basic symbol marker like this (Or page 105 of the latest published version of the Tome, if you have that)

Yes, you have to go through :ICON_CATALOG: to open it if it doesn't show up in the list of catalog settings, but once you click that button and get the Symbol Catalog dialog, you have two options, either find the .FSC file for the catalog (@Symbols\Cities\SS6\MS Color\SS6C_Ruins.FSC) and open that, which is the right approach and loads the actual catalog with all the symbol behavior, OR navigate all the way into the artwork directory (@Symbols\Cities\SS6\MS Color\Ruins) pick an image file, and hit ok, which is the non-optimal way, as it will just populate the symbol catalog window with the images in the folder without any symbol behavior like grouping, because all that is stored int he symbol catalog file.

From your screenshot it looks to me like when you are loading the symbol catalog, you are going into the artwork folder itself, picking an image and hitting OK instead of loading the .FSC file in the parent directory.

The reason this is important is that all such settings are store in the symbol catalog file (the .fsc). Going into the artwork folder and picking an image is an alternate way of getting the images into the symbol catalog window that is best suited for when you have a folder full of artwork that has NOT been made for CC3+, i.e. it doesn't come with a symbol catalog file. But loading it this way just loads them as "dumb" images, nothing of the smartness of the CC3+ symbols will come with.

So for any official or properly prepared CC3+ symbols, always load it through the symbol catalog file, not the artwork folder.

Yes and no.

The default grid command in CC3+ can't create such grids, but you have some options.

1. Make grid, then simply rotate it (You may need to unfreeze the layer it is on first)
2. Use symbols, these are rotatable.
3. Use a symbol fill based on some simple line symbols. You can specify rotation for this type of fill.
4. Use a fill that contains a rotated grid. If using a raster image, you can rotate it either in an image editor outside of CC3+, or you can use a shaded polygon inside CC3+ to apply rotation to the fill.

All of them require some manual work, as drawing at an angle like this isn't something CC3+ has tools to do directly.

Note that since CC3+ can't have a rotated snap grid, you may wish to simply draw it "normally" first, and then simply rotate the entire dungeon with the rotate command.