Getting lighting to look right and yet still leave the map usable is a tricky balance from my limited experience. In an environment such as you've drawn so far, the lighting would be likely good and fairly uniform flat, or largely none at all, for each particular area, so it may be worth asking how many lighting effects you really need before embarking on setting it all up.

I think this may be what you need to see/read.

Sue's advice is excellent for adding your own clouds.

If you might be interested in using symbols instead - or as well as - you may like to see the Alyssa Faden style pack, which was part of the Cartographer's Annual in 2014, as that comes with a number of cloud symbols designed specifically for use on overland maps.

If you find you've placed a door the wrong way after it's cut the wall, you can simply move the door symbol so it's the way you need it.

You can also turn off the Smart Tracking by clicking the check box in the Symbol Parameters pane (right click when you have the symbol on your cursor). This will stop the door aligning to the wall whichever way it wants (which may cause problems if you're trying to get the door properly aligned with the wall, however). It will still cut the wall as normal, while you have control over how the door is placed.

If you click the Disable Smart Symbols box, that will stop the door from cutting the wall at all.

This applies to all the Smart Tracking wall-cutting symbols, incidentally not just the doors.

This is the link for the Cartographer's Annual issue JimP mentioned, although as you'll see, that's intended primarily for drawing a randomly-created night sky as seen from a specific planet.

However, you could use the same procedure as in that Annual issue to construct a random basis for your galactic-scale star systems map. That was done using the Symbols In Area command. Resident mapping expert here Remy Monsen presented this as the last of his 52-week Command of the Week series of written tutorials that ran throughout 2017. You can find that article on the Forum here.

Of course, all that would do would be to place an appropriate number and type of symbol randomly over whatever area of your map you'd chosen. It would then be up to you to decide what the details were for each system (though by using different symbols, and assigning types of detail for each symbol on a separate key list, you could make a start on that process).

Symbols In Area is a useful tool in many respects, because you can vary all the random parameters as much as you like, and by drawing different areas, you can add different populations of symbols to different places. For instance, if you wanted a greater density of star systems in one place than another - along a galactic arm, say - you could just draw a suitable polygon shape wherever you wanted the arm to be, and then add a selection (or selections) of symbols to that area alone.