The thing limit is still there. KeeperFX handles that better than DK does, by simply removing unneeded objects so that important objects like gold and creature spells can still be created. It should only become a problem when you build a truly massive dungeon and create lots of traps and whatnot, and have enemy keepers do the same.
And indeed, I did not see your edit on the question Adam already answered. I changed the removal of the sidebar from 'Tab' to 'Ctrl+Tab' because people often came here complaining their sidebar was gone and that this was some kind of bug. This because when Alt+Tabbing out of the game it would also close the sidebar.