Suggestions from yah boi

The window doesn't seem to have anyway of shrinking it so it defaults to a 1920x1080 window.  This causes the taskbar to overlap the window.
http://prntscr.com/7ia0ob

Maybe have the movable windows overlay the model screen so you don't lose them.
http://prntscr.com/7ia1sx

A help and or info area that shows your YouTube channel, Moddb page, Forum, ect.

A hide and or minimize button for the Properties and Toolkit Window.  When hitting the hide or minimize button causes the model screen to re-size to the new layout.

Fix this:
http://prntscr.com/7ia34b
Basically when moving those windows around causes Windows Solitaire effect.  Cool but in the way.

Under the Windows drop down [That you don't have yet], be able to have a multiple or single window selection.  Similar to GIMP's
Single: http://prntscr.com/7ia3im
Multi: http://prntscr.com/7ia3r2

Have this empty spot for quick access to options:
http://prntscr.com/7ia3yt


[EDIT]
Maybe modernize the UI just a bit.