@FrankHowardNUSA Stock Railcores use a Duet 2 or 3 mainboard only, no additional CAN connected boards, as far as I can see. Anything beyond that is a 'custom' setup, and is going to require you to configure and maintain the setup yourself.
However, this forum (and the Railcore Discord for more Railcore-specific questions) is here to support you, and the latest version of the configuration tool should get you most of the way in setting up the machine; see https://configtool.reprapfirmware.org/
For your actual choice of boards, as the mainboard is only running the Z axis, if you are using the LDO-42STH40-1684MAC NEMA 17 motors (1.6A), a Duet 3 Mini 5+ would be plenty for them.
For the X and Y motors, a NEMA 17 motor (the same as Z) is specified in the BOM; is there a mod for NEMA 23 motors? 2 x Duet 3 M23CL closed loop motors can be used if so. The 6HC and Mini 5+ support them.
For the toolboard, as you want a scanning Z probe, you may as well use the new Roto toolboard. It would be capable of driving your Bondtech BMG and Mosquito, as well as having the SZP (and accelerometer) built in. You may have to create a custom mount for it on the toolhead, though.
For CAN connection advice and cabling, see https://docs.duet3d.com/en/User_manual/Machine_configuration/CAN_connection
Ian