difficult choice but I would take the SSD first probably as that has an impact on system responsiveness. You will want a 512 GB model as they are the best for capacity/price ratio right now.
You dont absolutely need a new board for overclocking right now as the CPU is recent, maybe when you get more funds months from now, and faster memory as 2133Mhz may not be able to keep up to give the best results. Idealy, 3000Mhz mems, at least 2800.