Question on if my build could be better

[Nord Kitten]

I am currently looking to upgrade my PC, specifically my CPU, motherboard, and ram.
I have experience building my own computers, however I have made mistakes with actualy picking parts before (not on compatibility, but just what I wanted to do with it.)
so I wanted to ask about if the build I am thinking of is a good one, and any suggestions that could be made to improve it. (I am making this for gaming, rather than rendering)

intel Core i5 6600K 3.50 GHz Quad Core
Patriot Signature Line 4GB DDR4 DRAM Module 2400 MHz ( i would be getting 4 sticks)
and ether
MSi Enthuastic Gaming intel Z170A LGA 1151 DDR4 USB 3.1 ATX Motherboard (Z170A Gaming M5)
or
Gigabyte LGA1151 intel Z170 ATX Motherboard ATX DDR4 NA Motherboards (GA-Z170X-GAMiNG 5)

as you can see, two motherboards are listed, because im haveing trouble with what one to pick.
I want upgradability with this machine, as well as the best price for performance obviously, and I don't mind getting used parts as well given I don't believe that has much effect on these specific parts.

 

[kanewolf]

I wouldn't buy 4GB DIMMs. 8GB is getting tight for gaming. You want a matched set of two 8GB DIMMs.

Used motherboards are something I wouldn't want. WAY to easy to bend pins in the CPU socket.

 

[Nord Kitten]

I wouldn't buy 4GB DIMMs. 8GB is getting tight for gaming. You want a matched set of two 8GB DIMMs.

Used motherboards are something I wouldn't want. WAY to easy to bend pins in the CPU socket.

I would be getting 4 of them, they are just the cheapest ones I could find probably not the best reasoning for ram, but they were better than a lot of more expencive ram that I looked at as well. Thank you for the advice with the motherboard as well, but you can fairly easily break a lot of components if you don't take care of them so as long as I'm careful with who I buy from it should be ok.