1. Same power plug you find on the Yaesu FT-817ND
2. I use the Palm. Works for me. I also like the American Morse DCP iambic paddle. I use the DCP with my Hendricks PFR-3. Yes I am a QRP CW rig collector!
3. I have 2A and 1A AGC and ATC fuses in holders terminated in Anderson Power Poles. 1A should work as maximum TX current at 12 volts (don’t exceed 12 Volts) is less than 1A. Consult the on-line LNR user manual for the MTR3B. The PFR-3 manual also has good info. Remember, not high SWR protection built in. Don’t exceed 12 to 12.5 volts. Use a buck regulator or 2 Zener diodes in series to reduce voltage of full charged gel cell battery. This is in the original PFR-3 manual and the MTR-3B manual.