Hi @pmjackson ,
You can put multiple BSP versions like the one I shared you which is in staging. In my experience, it has side effects though specially if there is overlap. I preferred not to use BSP json links that points to same FW version. @beegee might have more helpful insight idea since he got many experience already in creating BSPs.
As for Arduino IDE version. I have the legacy 1.8 as well as the 2.0. I rarely use the new one unless necessary like for customer support or if documentation needs it. Whatever version you use, both should be able to access the board packages. You do not need to install a separate one.