Building a New Listening Room on a Budget

My wife and I have been considering our next home, and recently signed a PA agreement with our builder.
The basic layout of the house is set but not finalized, which should be done within the next week.
I will have a dedicated room for my audio needs.  It measures approximately 25' x 14', and is not a perfect rectangle.  Doing my best to describe it, there is a 14' x 14' square section on one end and a 11' x 9' section on the other.
I plan to set up in the larger section, and use the smaller section for record/music storage.
The utilities room for the house is in the adjacent room, and I plan to have the internet router in that room and run a LAN cable from there into my listening room for streaming purposes.  I already plan to have at least one dedicated power line installed.  Should I add a second?  And, should I do 20 amp or 15 amp?
I'm planning to insulate the ceiling and walls adjacent to other rooms inside the house to avoid disturbing my family with the noise.  The floors will have carpet and walls will be traditional drywall.  
Beyond these things, what should I focus on that will not cost a ton?  I have read Robert Harley's article on his dream audio room build, but he spent way more that I'm willing to.  If I had to put a limit on it I would say around $10K.  
What other areas should I focus on?  
Thanks in advance!
Peter