For the motherboard, Gigabyte is just one of those having a good name. I've been as happy with mine as you have been with yours for the last decade so it was a natural choice for the price. Asus and MSI build good boards as well. The main specs I'd look for are Japan/Military capacitors for durability and a Z### chipset for overclocking capability, plus full size ATX for expansion cards and better cooling due to larger surface area. Also, if there's a bunch of boards with a slightly different ending in the name, I'd choose the cheapest one unless there's a feature I'd definitely want. The chipset tells the speed of the motherboard buses, add-ons like Wi-Fi, not to mention lighting only add to the price.
For the manirelli build... I'm not a great fan of liquid cooling, partially because transporting them in winter conditions for hours to meetings might cause freezing, potentially harming the hoses etc. For the same price you'd get an at least equally powerful and more silent Noctua air cooler. The pros and cons of SSD's have already been discussed in this thread as well as the size of a HDD. The video card... There's been talk that the 20## series is way overpriced compared to the performance gain over the 10## series. There's new features which may or more likely may not become mainstream in games. Instead of a GTX2070 I'd choose a 1070 and save $180, or a 1070Ti and save $120. That can be upgraded in the future if needed.
