8FG - limit v travel:
Limit is the maximum the throws of the channel can go with mixing, and travel is how far it will go from direct input control. Unless you specifically want more throw through mixing, just set limit and travel to the same amount. 100% is usually fine (ideally you'd want to match it to how far you want your servos to travel), then use dual rates to limit travel otherwise.
8FG - Trainer FUNC - You mention trimming out the buddy box. With all channels set to FUNC this should not be necessary. Make sure that all the settings on the slave transmitter are at their neutral defaults. The slave transmitter will then respond to all the mixes and trims of the master. Trim your model out with the master transmitter and the model should automatically be in trim when you hand control to the slave.