I am assuming by scamcast you are meaning comcast... if you really feel this way about comcast, I suggest cutting the cord entirely as they are much more liberal with their programming than other providers. With comcast most content is just encrypted (including the locals in some markets and that is expanding) and is not protected so you will only need WMC for premiums such as HBO, SHO, MAX, etc. all the other channels are marked copy freely so can viewed and recorded by other applications. Generally wifi isn't recommended for tv viewing and recording as you will have dropped packets, it is just the nature of wifi and the use of udp. Any non-protected recording can then use tcp for delivery over wifi and allow buffering. "HBO" however will require the use of WMC and can only be viewed on the machine that recorded it or WMC extenders (such as the xbox) connected to that machine (again over ethernet... extenders also use udp so wifi isn't recommended.
I would still plan on using WMC to record., though if you check out the xbmc forums/wiki you can probably find another backend for all but "HBO". I have no problems sharing the non-protected recordings with other devices but on TWC and cox all my channels (except locals) are protected so using
Your number 4 "statement" (as your only question in there was about usb 3.0) seems out of place... in the case for wifi, speed isn't the deciding factor as the problem is with quality of the signal and not getting interference, including other devices on your wifi network that need to "talk" from time to time and a drive there does no good for tv recording (you may wish to move programs to that drive if there is a good dlna server built into the router but it is far easier and more versatile if kept on your main machine.