Well put MR. @BoRRoZ,
I am not expert, but this I know you want help, you better be able to explain in detail what it is you want to do and what resource you got at your disposal.
Ah on the subject of using different nodes. You will have to do some kind of handover (as @BoRRoZ pointed out there is globally available frequency) , which is not exactly something LoRaWAN cares about as it was never designed to operate in such conditions. Furthermore you will be incredibly power constraint so you need to design some kind of mechanic to make use of to determine when you will be switching to which frequency.
Also seeing how you probably want to go for max range/power, might be a good idea to go for the EU433 (less attenuation and less power limitation due to regulations, you can actually have a PA in the node there, should help nicely with range).
Honestly the project has insane engineering problems to solve, at least from my perspective. It is incredibly cool, however very complex. I would expect that you define the system parameters in detail and than start thinking of implementing a particular scheme/device/code, whatever.
To me it would make sense to first identify what would be the possible issues that might arise in your particular case. It is unlike any LoRaWAN setups commonly depicted in the communal projects I have seen in the past year. Thus it will come with its own specific set of setbacks that you have to identify before proceeding as this is a system that will quite literally be beyond serviceability for its lifespan so to say. Thus you make damn sure nothing fucks up, and mate you will have a fucking LoRa node flying around, a ton of ■■■■ could go bad, ahaha.
So yes do let the nice people in the forum who can help (I do not mean me of course as I have mentioned no expert here) know exactly what it is you are doing.
Still your project has to be the coolest, most insane LoRa thing to date. So jealous I did not try to make it first, ahaha.