b350/450 for overclocking - a320 - for no overclocking (the XXXXG is not a 4.0GHz overclocker)
yes, a lot of the older b350 will not be compatible with the 2200/2400g CPU as their UEFI is not ready for these new raven ridge CPUs. either find a current up-to-date UEFI (noted on the outside of box 2000 ready) or can participate in amd reflash program.
no, would not be best suited to purchase 2200g if already got dGPU. need something cheap to get by on till money saved for what CPU wanted, yeah-maybe, otherwise the r3 1200 (you can use any mobo without 2000 ready) and be off gaming.