You realy should look at nRF24L01+, that level of protocol all implemented in silicon, ACK, node address, retry, multicast, ACK with payload, automatic packet assembly (CRC, preamble, address), dynamic payload length, pipes, the list is endless, and all for practically no money $1.50/£1 per module on ebay. Several different modules are available, PCB, ceramic or exteral antenna, some with PA/LNA some without.

George