I think the theater room would look more spacious if you put the screen much closer to the wall behind it and put cabinets, etc. on the side or back of the room or out in the "lobby" behind the room.
I would go with Plan 1 (bigger theater room) for the back wall of the room. At least so related stuff (DVD's etc.) can be stored inside.
That said, there is no compelling reason to make a theater room particularly large unless lots of people are going to be in it or you have a massive collection of DVD's (and/or larger videos like laser disks and/or VCR tapes), or books if say, the room is also going to be a library.
A medium sized screen 8 feet away is equal to a big screen 15 feet away.
Off topic: I think the idea of going through a bathroom to get to any other room is abhorrent. Better IMHO would be a corridor going past the bathroom to get to the bedroom and a bifold door opening inward into what remains of the bathroom. A compromise between your Plan 1 and Plan 2, regarding the theater side wall, might provide a better direct corridor to the bedroom.
Home theater hints:
Constructing a Basement Home Theater