How do you rotate/align all doodads for symmetry ?

[Chucky]

I made half of a map and I want to mirror it but I can't get all the doodads to align exactly how I want them. I can barely mirror match the terrain and it doesn't help that pasting all those doodads causes horrible lag on my PC. How am I suppose to paste and align them exactly ??? I'm losing my mind here...

 

[FeelsGoodMan]

Press "G" to use the grid. The grid helps you in aligning the doodads correctly. Then use CTRL+Mouse to rotate it, or simply just double click the doodad and change its rotational degrees.