Let's start with the basics and the SINGLE MOST IMPORTANT THING WHEN BUILDING A HOME.
PREWIRE, PREWIRE, PREWIRE, PREWIRE!!!
One shot, and one shot only, you can't easily get into your walls after drywall and insulation is in place to add wiring so you gotta do it now.
For a comparison, my (nice), setup includes about $3,000 worth of prewire labor. That includes lan, phone, data, video, conduit, speaker wiring, etc.
CONDUIT! Wow! What a concept! Thinking of putting a plasma over the fireplace, but don't want to put it in yet? Run a little plastic pipe (1.5" inner diameter minimum!) to the location, then run wires later if you want.
As long as you put the speaker wires in place, then you can put stuff where you want it later on as money and needs allow. FYI - I have 9 zones of audio setup in my home right now and wiring available for another 7 zones. Every room, every floor, everywhere. More than you need? Sure, but it may help with the resale to have wiring and conduit in place so you can retro things in later to your hearts content.
Not sure of the house setup, but including conduit to the attic is something that I would consider 'vital' as well. Antennas and attic access from your 'equipment room' location is key. It allows you to add a satellite dish, or run extra wiring as you need without going up the side of the house.
10% is not an unrealistic number to spend for most people on their low-voltage setup. But, it may be a bit much to add at one time, so why not maximize your ability to expand?
I actually was very surprised with the quality of the AudioSource 8" speakers that I picked up on eBay for under 100 bucks for the pair and put in the ceiling in my garage. They sound perfectly good in that less than stellar environment. Makes me think I may add them to a few more rooms around my house.