One should also remember that government employees with privileged access are people, and people can misuse the access they have.
We should recognize that the Fourth Amendment of the US Constitution was created to prevent this exact scenario. Law abiding people encrypt sensitive information to protect it from misuse by criminals, but the information can be misused by ANYONE with access.
Dividing a backdoor key between multiple parties simply creates a requirement that all parties agree to access the information before it can be accessed. It doesn't guarantee that the access will be lawful.
I have Ubuntu Linux on all of the above mentioned Dell laptops and the only issue I've encountered is lack of networking capability (both WiFi and Ethernet) while using 12.04 on the M4800. This can be fixed by loading a newer kernel (3.13 instead of 3.2). The newer kernel is directly available from the Ubuntu repo, but obviously you need a network to do that. A quick workaround to get the networking going is to use a USB-to-Ethernet adapter for access to the repo. There are no issues with 14.04. Dell is still shipping 12.04 (they haven't upgraded their standard image to 14.04 yet), but their version of 12.04 includes the Dell patches to make everything work.
Iproute2 has worked out very well for me for a quite a long time and I have no need to run any additional routing daemons.
How will this rig differ from HackRF One? (I bought two of those last year.) I see that one of the goals is to get FCC type accepted so I guess it will probably have better filtering to reduce QRM. (HackRF doesn't have much of anything.) The HackRF goes from 30MHz to 6GHz with 20MHz of bandwidth and has an 8-bit ADC/DAC.
I'm also curious what one would use to operate an SDR transceiver. I haven't found any suitables application that make it easy to transmit with the HackRF. There are plenty of SDR receiver apps, but nothing that makes transmitting easy. Do you know of anything?