On the end-node you only need to enable ADR.
This will signal the network server to control the device datarate based on SNR. This will happen inline with sending uplink packets.
When the network server determines that the device may use a higher datarate or lower power, when at max datarate, it will send a command for the device to change settings.
The ADR step can be used to adjust the aggressiveness of datarate switching. Theoretically there is a 25 cB link budget difference between each datarate. Therefore the min value for ADR step is 25 cB. Default value of 30 cB is used to allow a small variation of SNR. Higher values will require greater SNR to reach the highest datarates.
DR4 is the default max and the maximum uplink datarate in the US/AU channel plans. DR3 – SF7BW125 and DR4 – SF8BW500, the bandwidth is 500k which more 4x faster than a 125k channel. Each SF or BW step will double datarate.
The link check does NOT need to be called in order for ADR to work. It is merely a way for the device to query the network link health. The link check could be used by the device to implement manage its own datarate in similar fashion to ADR but this would not be AUTOMATIC. Managing ADR at the server is more efficient as downlink packets will be minimum.
When ADR is enabled and ACK is requested with >2 retransmissions the datarate will be lowered after 2 missed ACK’s. The ADR check will not allow ADR to lower the datarate below the minimum required to send the current payload size. It will NOT automatically increase the datarate to match a new payload.