Rangefinder Hover in Guided_NoGPS mode

Having scoured the forum and the docs, I have come to the conclusion that I need help.

According to this:
http://ardupilot.org/copter/docs/common-rangefinder-objectavoidance.html :
" RangeFinders (Sonar or Lidar) can be used for Object Avoidance in Copter-3.5 (and higher) in Loiter and AltHold modes."

but, http://ardupilot.org/copter/docs/ac2_guidedmode.html#guided-nogps says :
“… This mode was created for use by companion computers that may want to fly the vehicle as if it was in AltHold mode.”

but then http://ardupilot.org/copter/docs/common-rangefinder-landingpage.html#common-rangefinder-landingpage goes on to say:
“Downward facing Lidar are used in flight modes which have height control, such as Altitude Hold, Loiter and PosHold Mode.”

The documentation is a little bit unclear on this IMO.

I am developing an indoor 360 Lidar position hold algorithm using RPLidar and ROS, and my hope is to use the existing Altitude Hold and collision avoidance mechanisms with two MaxBotix. One pointing up, one pointing down. I would like to take-off from the ground and hover.

A key problem here is that I don’t have GPS, and would like to use my raspberry pi mounted on board to send ATTITUDE_TARGETs to steer the drone. For this, I would want to be in Guided_NoGPS mode, but I am unclear on:
-if I can take-off in this mode (and how, in a mavros python environment),
-if I can hover in this mode using a downwards facing maxbotix,
-if I can avoid hitting the ceiling in this mode using an upwards facing maxbotix.