The actual difference is that the 2x4GB 2400MHz kit is somewhat faster because it can run in dual-channel mode and at a higher frequency. The real difference is, well, none. Get the cheaper choice of the two.
I would not recommend getting the parts you mentioned (specifically the CPU and motherboard). The board may require a BIOS update to use the Kabylake chip, and without a compatible CPU you'd have no way of doing this. Suggestion: Get a Pentium G4620 with a H270 board instead. The G4620 supports hyperthreading, placing it in the same performance range as i3s, but comes at a much lower price. With a H270 board you wouldn't have to worry about compatibility.