Are you also minimising the game? For some reason the game does not like to be minimised. You can work around it by turning "running in background" off.

Those circle/halo/aura/idk things are the "love glow" which happens if you sit/stand next to a deer.

I had the same problem with crashing and just recently managed to make it work. Turn off the option to run the game in background, and turn on the option to run in a window. Quit the game and once you restart it, the box to run the game in background will (probably) be ticked again (that's what happened to me and I was like,, wut). Turn it off again and restart. Once you load it next time, it should work normally and you'll be able to minimize without crashing. Then again, I'm not sure if this helped me because of these settings or because I'm using a different computer with better specifications, but anyway, it won't hurt to try.

That's what I did, exiting by clicking on "quit". I can't change the settings at all, the box still remains unchecked when I next boot up the game.

The love glow is definitely cute, I had no idea it existed!

When you start the game, right click the icon and select "run as administrator". That may help with your settings issue.

Glad to help Choosing to run as administrator usually fixes most problems. I recommend making it your standard way of opening TEF. You can set it so that it runs that way automatically so that you don't have to remember to right click every time, too. Right click the icon, select "Properties" and then go to the "Compatability" tab in the window that opens. At the bottom, check "Run this program as administrator" and click "Apply"/"OK"

I almost always start out with a set that I like, and then make a design based off of it. Or I'll work with a design and keep the set pieces in mind as I design it, so that I'll have something to use when I put the deer in.
Some deer I just let wear whatever gets thrown on them, although they have their favorite pieces!
For example, Laurel was a white and red base (koi) with matching antlers (secretary bird) and no mask or a white mask (barn owl). I knew what color scheme I wanted, and I used that to design something that could be represented by the in-game pieces.

Some people design first and then just use whatever set they think most closely fits, even if there isn't a set that's particularly close (for example, many red deer will use either the Noh pelt or the monarch pelt, since we only have oranges and no reds; black deer often use the space beluga pelt or DotD, since we don't have a solid/non-colorful black).

Some people make a challenge out of putting together a random set and then drawing inspiration from it.

It really depends on how you like to do it!