Let me give you the quick answer first then I will explain everything in more detail.
1. Go with Cat6 or at least Cat5e.
2. Whole house audio isn't crazy and doable, this will need more explanation so see below.
3. Home Theater is a great way to socialize, watch films with family/friends and of course enjoy a great BYU sporting event. Doable.
4. DSS wiring can be done by you no problem. RG6 Quad shield runs are what is needed. Centrally located as well is the key. That design scales to meet YOUR family needs and not the needs of the installer. You basically made the installer job 100x easier by designing it this way.