We are moving....well actually moving and replacing a bathroom door. The wall that the vanity will be on is too short so therefore...break out the saw and make the wall longer. Anyway, the wall is much thicker than a standard wall at approximately 8 inches. We noticed that the pre-hung doors in the stores use wood that is wafered together to create the casing. We want to use stain on pine trim and therefore stain on the door casing BUT that's not an option with the whole wafering deal. I can't talk my wife into paint so we plan on building our own. Does anyone have any tips, insights or direction for us?

Most retailers carry both finger jointed, & good old-fashioned solid wood trim. However the Big-Box stores will not normally stock anything but inexpensive pre-hung units.
You may have to spend a few more bucks, but ask a few places for a pre-hung unit with a non-finger jointed jamb.
If they have pine veneered, that would be best, as the stain job will turn out best. Under the veneer is still finger jointed wood, but at least it is hidden.
Retailers will not stock any Pre-hung units with 8" jambs.
You will have to add a pine 1X4 jamb extension to a standard pre-hung unit.