And what is the location of your monitoring(mobile, base, portable). since sdr is really not portable and again a totally different learning curve probably more complex than the g series radios. But it has no keypad!😊.
We can’t hypothesize about how many theoretical dongles it will take without specifics.
Each of the $25 RTL dongles cover 2.4Mhz of spectrum (control and voice frequencies). The more expensive cover up to 10Mhz of spectrum (maybe some cover more?).
I can guarantee you’d need two dongles to cover any bite of both vhf and 800. The required count goes up from there.