CDL can be switched in or out at speeds up to 100km/h.
Switching between 4H and 4L can only be done in Neutral.
Front and Rear diff locks can be switched in only when in 4L, and at speeds up to 8km/h. They should disengage automatically when put into 4H.
Cigarette lighter socket would be fine, but the 50A anderson plug may be pushing it.
Richard's Auto Electrical in South Australia do provide kits for the 300 rear fusebox.
I use a ScanGuage 3. It will do ATF temp. I don't know if it does engine oil temps.
ScanGuage 2 will only display 4 entries, oposed to 9 for the newer SG 3. It is also less capable.