Building a house

+1 to Russ' comment.

Separate electrical circuits. Ethernet of course. Look into "Rockwool" or similar sound insulation techniques and see if that is of interest.

--10g dedicated line with quality outlets. (Unfortunately some codes require crap safety outlets so you may need to swap these after inspection)  
--if using led lighting, place on a separate line.  Carefully consider lighting options. Ceiling cans are nice for task lighting but I do not like them for when I listen to music.  Have some nice accent lighting options.
--carefully research room dimensions and where you anticipate speaker and listening chair placement.  Can be hard to predict but clearly some dimensions will have fewer standing wave problems than others.
--do you want windows?  I opted out as they are not nice acoustically and I wanted to achieve acoustic symmetry as best I could.
--suggest double dry wall with a layer of "green glue" adhesive
--Crown molding in acoustically your friend.
--Use a solid, heavy door to the room and a seal on the bottom is suggested as well.

1. Double wall construction with staggered studs (one wall's studs DO NOT touch the other, greatly reduces vibration transmission.
2. Line inside of walls with sheet vinyl. 
3. Double sheet rock on inner walls.
4. Electrical outlets close to ceiling to allow for wireless speakers. The more the better.
5. take steps to make heating/cooling as quiet as possible.
All I've got...

good advice given here... only thing i would add is to add a large storage closet to have room for extra stuff, and don't forget how you will do wall hangings, curtains and such for proper room treatment

https://www.homedepot.com/p/Siemens-FirstSurge-Power-60kA-Whole-House-Surge-Protection-Device-FS060/...

Surge protection at the electrical panel level