i am really a newbie in ics but here is my thoughts, may be u find them usefull
it seems that u should start with a specific standard to work on , or if u r not targeting a standard then u should chose some free band ,in the first case this should chose everything for u "carrier, number of channels,, min. SNR,,,etc",
for the 2nd case i guess u would have "Some" degree of freedom but not that much as the band is limited and there are some regulations like FCC for somethings like leakage for instance.
if u are like making ur standard , "well congrats
", but this will have to be limited by many aspects like type of data u r sending, the number of users u expect, this should say what is ur modulation scheme and BW ,, u should also put some power limits "limited by the battery",,,,u should estimate some distance limit u want ur Transceiver to work on, this might put other limits on power and min. SNR also might have some effect on BER "related also to modulation scheme used and type of data u send",,,,,then u should also see some rules from FCC like leakage and blockers ,,,,,,,,,,,,,,,,,,probably much more that i don't know.
wow this seems really big complicated job and seems need really experience Dudes for it.