Obviously, you have to decide on AMD or Intel before you buy a board.
And you have to decide on the board before you commit to a particular CPU....whether AMD or Intel.
I would NOT buy the board before the CPU. If you buy a board in March and a CPU in May, you wouldn't know until May that the board you bought 2 months earlier was dead on arrival.
I'd certainly try to decide on the specific parts before buying ANY parts. Stockpile the money for several months if necessary.
Not a major reason to move away from DDR 4 as long as the DDR 4 you have now is compatible with both future board and CPU.