To try and answer your queries:

1. The Honey Badger ran a 1mm thick Aluminium door finger plate along the front of the HDPE wedge and that did OK when the plate was wholly on the wedge as it was supported. At the Maidstone 2017, I moved it forwards and put it on hinges much to the same effect as you plan and it buckled horribly. I could straighten it out with a hammer but really, I'd advise against it. Steel might be better but I don't think it'll stand up at 2mm.

2. I use a wooden cradle with no straps and that has always been OK. It needs only to keep the robot off the ground and be stable enough so that if the drive wheels do spin, it doesn't come apart. Mine is very wide to allow for this.

3. Ask the event organiser on that one. I recall Luna-Tic asking this for the FW championships in 2017 and RoboChallenge said they didn't but this is one of those times where the event organiser needs to determine this. However, if in doubt, assume it does.

4. Yes. One of the tech checks is to check for exactly that (i.e loss of signal = no movement).