I have installed the B2B from Sterling with a charge current of max 120 amps.
However, I do not use the ignition signal to turn on the charge booster but have used a radio controlled relay to turn on the charge booster whenever I need it (and the engine is running). I charge the LiFeYPo4 almost exclusively with solar power or mains power, rarely using the alternator/charge booster.
What charging power is needed also depends on how much power you want to charge into the battery via the alternator. If there is sufficient solar power and/or mains power and the alternator is only needed as an emergency solution, 30 amps should be quite sufficient.
Roland