I’d guess key is: how many transmissions do you expect? And can your application work with packet loss? (With LoRaWAN you should always expect to have some packet loss, even when no collisions would occur at all, if only as the current gateways are half-duplex so cannot listen when transmitting a downlink.)
See How many gateways are needed to support 1,000 nodes sending 10 bytes per 5 minutes?