How do I get my blower motor to turn on with my new hydronic coil heat?
You need the wiring that turns on the pump to also turn on the fan. You may need to add a relay to isolate the fan from the pump due to different voltages or any other problem that could create. You could also use a temperature controller to run the fan which is how commercial installations do it. A controller like the " honeywell  T675A1425" or a " White Rodgers 3F01-111 could be used, They would turn the fan on and off when hot water is present.