It's technically possible, but please don't. The restriction for image sizes in posts are due to many people browsing the forum either with a slow connection, or with limited data plan. When someone visits a post with an embedded image, they don't get a choice if they want to display it or not, which is why the large versions of the images should stay in the gallery which require a conscious choice to view. You can link to the image in the gallery from the post instead. (Just don't put the link on a line by itself, the forum post editor software takes that as a sign it should be embedded instead of linked.)

Hmm... Old maps should normally work fine as long as you have the same add-ons as you did when making the map. I can see there are some spots on that map where the background shines through, so that is loaded just fine, but obviously there is a lot of things missing. Do you know what art you used when creating that map. Was it standard CC3/DD3 art, or perhaps you used some 3rd party art like the CSUAC package?

You can gather clues from the file names. You can find symbol filenames by opening the symbol manager, picking a symbol and hitting the lsit button, while fill style file names can be found on the bitmap files tab on the fill style dialog. If you post the .fcw, I should also be able to tell you pretty quick.

As for your CC3 dungeon question. CC3 Dungeon is just a very limited dungeon style, more like a demo than a proper full style, only allowing you to make rather simple dungeons. As such, it doesn't have a lot of symbols, and all the symbols are already loaded in the symbol catalog window, the catalog buttons at the top aren't connected to the style at all, and just load catalogs from a more or less random style.

Yup, it's the rendering pass. Increase the pass size.

Turn off the demographics coloring: City -> Layers -> All BLDNGs with shading

If that doesn't work, try hiding all the layers that start with BLDNG

Still about a week left of the competition, which means it is still enough time to pick and map a building (plenty of small ones available if you want to do something quick).

I'll also point out one thing to everyone planning to submit their map to the atlas too (hopefully most of you). The atlas has it's own navigation bar off the side of the map, so I do not need that little navigation box CC3+ makes for multi-floor maps in the lower right corner. Because I usually need to rename the map files when putting them into the atlas, the links in that box will be broken anyway, so I'll just have to delete it. So I would be pleased if you just remove the entire box (including the hidden hyperlinks (view -> Show Hyperlinks to show them)) before you hand in the map or at least keep in mind how the map will look when I remove it. Thanks.