Arrival is at the lower level. Departure is on the upper level. However, at the gate area, one goes back down to the lower level to board the plane (there is stair and a small elevator at each gate).
https://www.taoyuan-airport.com/engl...sit-procedures describes what happens and
https://www.taoyuan-airport.com/english/facilities_map has the maps.
I would definitely use the wheelchair service. The safest place to meet is probably the departure gate lower level (i.e. they take him all the way to the boarding area). The "earliest" meeting point would be at the corridor of one of your gates on the arrival level.