Here are a few things I would like to see:

• Freshwater lakes, cold
• Subterranean lakes.
• More vessels, both sunken and floating (boats, ships, rafts, canoes)
• Various standard dungeon items encrusted with barnacles, like chests, barrels, ship hulls, weapons, etc)
• More undersea monsters (clams, eye of the deep, jellyfish, drowned ones, sahuagin, cats, kuo-toa, dragons)
• More traps, both those meant for undersea use, and those in sunken dungeons.
• More ship-based items, like cannons (and balls), ship's wheel, bundles of rope
• Modern/futuristic items (Ships, boats, cars, shopping carts, bikes and items. Sunken starships are great.)
• Some bare treasure piles. The ones from DD3 are full of sacks of coins, which looks weird underwater.
• Varicolor versions. would love to make a dark mermaid.

Not directly. I recommend drawing around the settlements with the tool, then placing individual trees after that along the edges to give a tighter fit (And finish off with a sort symbols in map to arrange them properly.)

There is also the exclusion commands, this allows you to specify areas to exclude, but this only work with polygons, not symbols.

I am not even sure it need to go into a lake in the atlas. Honestly, it looks a bit more like a saltwater map, so I might just put it off a coast somewhere.

Coming along pretty nicely there. Always interesting to see how these drawings of yours evolve.

From the EULA: