There are many ways...
You can place all the midi regions on top of each other or above/below eachother in the Arrange and then select them all and click on Merge. Default KC is =
Also check out the Hyper Editor for programming drums - once you set up a hyper set, it's much easier to program drums by hand!
When copying and pasting in the Piano roll make sure your play head is in the same position when you paste as it was when you copy..or if you copy say all notes between bar 1 to bar 2, first place your play head on bar 1, select the notes and copy. To paste them between bar 2 to 3, place your playhead on bar 2 and select paste.
I find it easier to hold down Option and drag the selected notes to copy in the piano roll... hold down shift and you will only be able to drag the notes in one direction (i.e. vertically or horizontally - very useful!)