I want to somewhat future proof my pc a little. I have my graphics card ect ect

If I get DDR4 my budget is $350 for motherboard + CPU bc my actual budget is $500 and I need to get 16gb of ram

if I get DDR3 my budget is $400 for motherboard + CPU bc I have the ram I'll get a 2nd monitor

Putting aside the uneven comparison between the price you're willing to pay for ddr3 vs ddr4, they really only produce ddr4 CPU's now anyways, so ddr3 is out of the question completely if you're trying to future proof.

AMD: https://pcpartpicker.com/list/L9Gbjy

Intel: https://pcpartpicker.com/list/DDxRGG

What do u think about an i3? Apparently they're best vs value? But, I'm not going to run liquid cooling.

For an addition ~50% you get 50% more cores, plus a boost speed that's 400mhz faster than the i3, and 50% more L3 cache. An i3 will do fine for now, but an i5 will hold up a lot longer, and is well worth the extra money IMO.
However, personally I'd go for the Ryzen 1600 chip. For the same money, you get multithreading capability (essentially doubles your core count), significantly more cache on all 3 levels, a much better included CPU cooler, and the ability to overclock which will help you a few years down the road when it's harder for it to keep up. Motherboard are also less expensive for equivalent product lines.