Serial echo for 433Mhz RF transmitter

I'm kind of stuck at the line with all the ??????????????

I am, too. Were all those ? necessary?

    delay(2);  //delay to allow byte to arrive in input buffer

A load of crap!!!!!!!!

(Does the extra punctuation help? I didn't think so).

You need to read and store data until an end of packet marker arrives (the carriage return that the Serial Monitor can add is a good choice). When the end of packet marker arrives, then you send the data.