There is a description of the Intel hex file format in the tutorials on this site. I once did a similar project all by myself.
Checking Intel hex file integrity does not require a buffer, a running checksum and a location counter is enough, a state machine sort of approach will help you keep track of what the next byte will mean. Just to start you off, you will begin with state 0, which means "A : is expected".
About waiting for a space: An intel hex file already has a clear start condition, the ":"! It will not make uploading from your PC more userfriendly if you must first send a " " to the 8052 bord manually.