To elaborate a bit on Sue's answer. RAM is used for bitmap caching in the program, and is also important in determining the maximum export size of the map since that requires space in RAM for the work.

As Sue points out, it uses 4GB at maximum, but it is always a good idea to have that 4GB available to the program, which means that if your computer only have 8GB's of RAM you might need to be careful about what you run at the same time, while if you have 16 or more, it is generally not an issue. The ram allocation needs to be contiguous, so for a lower memory machine, it may need to be rebooted more often as well, especially if you find that CC3+ complains it doesn't have enough memory to complete an export.

You'll easily see if you have DD3 installed by creating a new map in the dungeon type, and see if you have the DD3 dungeon available (as opposed to just CC3 Dungeon).

If you don't have that template, it means you have forgotten to download and install the DD3 setup. It is a separate installer from the main CC3 one. It was included in the Humble Bundle (if you got the top tier), so you should own it.

I assume you scaled it up to that each minor flagstone became a grid square? That might be more than that texture can do. A texture have a limited resolution after all, it can't be scaled indefinitely.

However, it might just be CC3+ displaying the wrong resolution version of the image, that can also happen if you scale it by too much. Try going into :CC2RESMODE: and set the display to manual -> Very High and see if that fixes the issue.

The tiles aren't made to fit the grid, but if you change the scaling of the bitmap, you should find a value that should let it match up pretty well.

Just click the fill style indicator in the top right of the program window, and in the dialog, go to the Bitmap Files tab. Now, in the dropdown, find the fill you are looking for, and then changed the width and height scale values in the bottom right of the dialog.

The numbers are part of the grid. Probably the simplest is to just erase the current grid (You may need to unfreeze/thaw the HEX/SQUARE GRID layer first, and then add a new one using Draw -> Hex or Square Overlay, making sure to uncheck labeling.

Well said. I'm in the same boat there, my free hand skills are non-existing, but with CC3+ you can just give it some coordinates and tell it you need an Arc. Gives a measure of control and precision no painting program can.