Hi,
Have you looked into the cc series from TI? There is a lot more to consider when making specs for a wireless link.
Range? Compactness - low frequency gives you longer range (6 dB more per frequency halfing), but the antenna must be larger to achieve good antenna efficiency.
So, in practice a higher frequency may yield longer range.
The smaller the receiver bandwidth, the lower the noise floor and hence the better receiver sensitivity. But this is at the expense of lower datarate to achieve lower occupied transmission bandwidth to fit the RX bandwidth.
Every packet for a normal FSK/GFSK based modem consist of a preamble, sync word, payload and CRC. Some require only a couple of preamble bits.
You could use 16 bits sync, but this would lead to a lot of false packets. So there are many trade-offs to consider.
I would read up on the basics. I use CC112X from TI. Read all the literature available on their site, and the e2e forum as a starter.