Doors and Windows - Interior Door question

I'm planning to install interior doors (glass pane - 15 lite pre-hung). The opening is 72" wide by 93" high, thickness of wall is irregular (6.75" to 6 7/8"). It is going to be a double door. The standard size pre-hung doors at HD is 32" X 80" for each door and requires a opening of 66.5" X 82". Anything more than this height is custom for which they want my first born. My question here is how do I address the gaps -

first the 5.5" gap on the sides (2.75" each side). Isn't it too big for shims? What do I cover the gaps with? Trim?

second the 11" gap on top. I'm confused as to how to screw the frame to the top. Even if I manage with a long screw and some wood pieces how do I cover the gaps? The trims I have seen are about 3 inches or so in width.

Is it a bad idea to try and do it myself? Should I call a carpenter instead? Any help on installation tips is also appreciated.

Thanks in advance,

It would work to add framing to the sides to close up the space. You could set a jack stud on the sides with the cripple wall overhead. Allowing an inch all around for shims for the per-hung door assembly.

here's howto:

http://www.kimberleybuilding.com/improvement_tips/how_to_frame_an_interior_door.htm

Since your opening is already there, you should not need a king stud. You would need to shim and fasten the jack stud to what would be the king stud for stability.

The hard part of the project will be manuvering the heavy double pre-hung unit.

It may be better to extend the sheetrock to the door opening than try to make trim work.

Hope this helps.