That's a nice & fairly cheap motherboard @ $99.99 USD. The reviews give it good marks too. It also supports fast DDR4 too @ 4133 (OC). Slap in a 2x8 FlareX DDR4-3200's and sweetness ensues. (My own personal pref on the RAM, as it's what I have in my own system and it's been absolutely great. Someone here may link to a better kit, but...
) I REALLY like the Bios update ability! If you get it and the 3700X does not work because it has an older Bios ver. from the factory, no worries. Get a USB & the newest Bios and Presto.
As for an aftermarket cooler, I'd stick with the stock unit that comes with the CPU until you are comfortable with tweaking your system. The same one came with my 2700X and it's just fine. However, if you want an aftermarket one, that's a hard one to answer and everyone and their mom will have one they think is better than the one listed in the previous post lol! Still, can't go wrong with a Noctua NH-D15. This brand knows it's stuff. For water cooling, I'd really stay away until you were very comfortable and had a good grasp on whats under your PC's proverbial hood. The Noctua I mention above kicks arse.
Don't ever go "budget" when it comes to cooling your CPU lol.. Either use the Stock cooler that comes with the CPU, or get a good, quality unit.
Not saying the one above is the only good one, just one of the so called best. If not that particular model, then the brand itself.