750w should be enough unless you ya know bios flash and shunt mod your card.

FYI although Arctic Silver 5 is a good paste (despite what morons will tell you), it's really not worth the hassle of cleaning off whatever paste is going to come on that Scythe cooler. At best you could expect to drop a couple C, but you're not going to be thermally limited when overclocking Ryzen with a good aftermarket cooler like this one, so that isn't going to matter. You're going to hit instability with the voltage instead. Tldr you don't need to buy it unless you're planning to be disassembling and reassembling your build

I'd look up reviews of the B3. I don't follow PSU's too closely but I feel like I recall hearing less than stellar reviews about that one.

if you meant overclocking the GPU, dont bother. its a blower card and there is too much heat generated that woudl prevent any reasonable overclocking.