.1. True Altitude = 9856.9 ft (7086.9 ft above station). This all assumes that the QNH was given by the station and correct for the station elevation.
.2. It depends upon the MEA. True altitude error is a multiple of the altitude difference between the reference station and the mean temperature of the column of air to the station Vs the ISA temperature of the column of air to the station. It is not a simple additive or subtractive.
.3. Single Side Band (As applied to HF radio).
.4. SAT = -40°C (Your TAS must be 275.4 Kt or M = 0.463 for a 10°C RAM Rise). Mr. Bernoulli, TAT is always higher than SAT.
Regards,
Old Smokey