You can press u on an object to upgrade it without using your mouse.

You can press the delete key on a strut to quick delete it, or press delete after clicking on a selected object to remove it.

You can press e/click twice on an weapon to make it fire at it's current selected position with a degree of inaccuracy.

You can hold Ctrl while placing weapons to prevent background bracing and doors for being removed, this also works while placing materials.

That's it for now.

if you didn't know I will tell you how you can place things.

you can place objects by left clicking a material

you can place a material by selecting a joint,moving the mouse outwards, and left clicking.

you can place a grid(I guess that's what it's called) by selecting a strut, and doing the same thing I said before.

That's it for now.