Yes, it supports DDR4.
Yes, it supports DDR4.
That's actually a good thing, you can get more than twice as much ddr3 than ddr4 for the same price
DDR3 costs are actually increasing now, the entire RAM shortage is really frustrating everyone.
You can obtain a 2400Mhz DDR3. DDR3 can reach up to 3000Mhz.