The B450 functions well without any problems when paired with the 3700X.
The B450 functions well without any problems when paired with the 3700X.
It's a good choice. The Tomahawk Max and Mortar Max provide continuous support for Zen 2 right from the start. That's what the Max means.
It should be okay even if the BIOS isn't installed on the newest MSI USB BIOS flashback. In theory, it can still function without a CPU in the socket. Just load the latest BIOS onto a USB drive and press the BIOS flash button on the board—power will be applied to the motherboard as well.
It varies by board; the B450 is mainly a chipset, not related to power delivery or other features.