I've had X1 for over 18 months and love it.
1. Maybe this is a question for Comcast but i do not see anyway you can block recorded content on all the boxes because they all share the same Comcast account. I see you can only set Parental Controls in the settings to prevent certain channels and content from being viewed.
2. Never had a problem with the DVR locking up. Never had to cycle the box.
2b. It doesn't matter as far as I know where the DVR box is. Everyone has access to it. Think of it as having an external hard drive on your network with pictures and videos. Anyone can get to it if the permissions are open. Comcast has all the permissions open on their boxes under one account.
Thats as much as I know, again it may be a question for Comcast. Also have my Slingbox 500 on my network and its awesome.