Your budget of $1000 will not reach for "6-8 drives", and unless you already have WHS license, you will need another $300 just for software. Windows does not need very powerfull CPU (I have mine installed on an Atom ITX board), unless your streaming will require transcoding as well.
I would go with big case (these 8 drives will generate plenty of heat), with good cooling (or separate storage enclosure with appropriate backplane). Finding a budget motherboard with 8 SATA ports will be also a challenge.