1) Depends on how powerful the Antenna is. Most Antennae usually have a minimum safe distance where you will be OK from exposure. Most modern Wx Radars are very low-powered and have very close safe distances. I believe the safety issues are dealt with in the manuals???
2) No, because the metal reflects the transmission which will be received by the Radar as normal. If it's a high powered Antenna and you are close behind though you may get a little warm
as may the occupants of the aircraft in front... as for the fuel tank however...
3) Not sure, I'm only an engineer, but I have heard that many switch on Tx when lining up for departure, others during taxi (there is another thread on this subject just now).
4) Don't know.