I'm in the process of deciding whether to take a mortgage, and build a new home on a piece of land I have been offered...or fix up an older home, built in 1942. Completely strip it and gradually work on it.

The questions I have are mainly methods to effectively make the old house energy efficient and air tight. I've read a lot about 2x6 framing, double stud walls, and separate exterior walls. I'm wondering what would be an effective method, after stripping lath and plaster from an exterior wall...ripping 2x6 and nailing them on the old 2x4, or framing a new wall, and slapping it up next to the old wall, possibly insulating the exterior wall, covering it with a rigid foam, then adding the new 2x4 wall, and insulating it? Should I try to draw a picture to explain?

In addition to the walls, there is preexisting insulation in the attic. I was wondering about adding rigid foam to the ceiling, either a.) tearing out the plaster and leaving the lath (so old insulation doesn't come out) and nailing up rigid foam, then sheetrock. b.)leaving the lath and plaster, nailing foam and sheetrock over that. c.) tearing it all out, including old insulation, then foaming, then sheetrock.

Thanks for any comments / suggestions!

Edit :
Climate Zone 5 (Nebraska)
Yes, there is a basement, no insulation, and some settled walls that cracked many, many years ago.
Windows are the old style, single pane, weighted sash sliders.