Lower bootloader section base by another 256b just in case.
Simplify nrf24 delays.
Switch to 2ms rexmit delays, 250kbps rates.
Make indentation more consistent.
Reliability: eventually give up waiting for nrf24 flags bits.
A software rexmit + SEQN machanism in addition to the one in nRF24.

Also change the delay before TX ops to 4ms and change the hello packet
format to match the flasher script: last byte is max packet size to use.
Lower max packets may be slightly more reliable in a low-RSSI setup.