[Discussion] Advice / Best practices for a dedicated PC for couch gaming?

I have a gaming PC that aims to be a self built Alienware Alpha / PC console, for couch gaming.

I've set it up so it auto logs in and launches Steam in big picture mode on startup.

I've set up the default user account as an admin, since lots of games were asking for admin rights at installation.

I've read that installing Steam outside of program files circumvents this issue, is this 100% fail proof?

I've seen people edit the Windows registry and replace the shell, changing it from windows explorer to Steam Big Picture, what are the benefits / drawbacks to this practice?

Any other tips are appreciated, I'm looking into making the experience as fool-proof as possible, since my cousin wants me to replicate my setup into a new pc he wants me to build for him.