@jenjane More questions are fine, although RGB is not a subject I've spend a lot of time learning about. It does tie in with the case though, so it's best to consider both at the same time.
First of all, I don't think the airflow is very good in the second case you linked. The first one is great: the difference is that it can draw air through the front panel and expel it through one of the side panels or vice versa; the first one has a much smaller opening in the front and only the small back panel fan for exhaust. Check the photos on Newegg and you'll see. The point is, in the first case, you could mount a 3-fan radiator on either the front or side panel, put three fans spinning in the opposite direction in the other, and get excellent airflow. There are other cases that have similar layouts, but it's hard to search for them: you really need to check the photos and sometimes even look up the dimensions.
Once you have a case in mind, you can plan where to put your RGB. Taking the example of the first case you linked, if you're mounting the radiator on the side panel (facing towards you as you look at the components), then you probably do want it to have RGB. If you mount it on the front panel, you may not notice RGB facing into the case, depending on the angle at which you'd place the computer. Many cases also come with RGB fan covers, basically grills that light up that you'd put on the front panel over the fans or radiator, and if you had those, you wouldn't need RGB fans facing out on the front panel.
Additionally, the fans that come with a radiator are more efficient than standard case fans. So while you could swap out the radiator fans, it's better not to, or at least to get (more expensive) replacement fans designed to go over a radiator. At that point, you might as well go with an RGB-ready radiator. If you want other options, Corsair makes excellent AIO (all-in-one) coolers too. I didn't pick any of them because the Fractal Design model is just as good and a lot cheaper without RGB.
Point is, you should choose your case, then where you want the radiator to go, and then you'll know whether you need its fans to have RGB. With the RGB models, you'll likely also get some lighting on the pump that sits over the CPU.
If you want a tricked-out system, you can also get RGB memory. In that case, decide whether you want two or four sticks: people typically get two, but four should be perfectly stable, and 4x8 GB is not much more expensive than 2x16. If you let me know what you want, I'll double-check the compatibility with your motherboard: most quality RAM should be supported, but it's always better to check first. And RGB RAM is not that expensive either compared to non-RGB options.
Most graphics cards have RGB, and most quality motherboards do too, but I can double back and check those as well.
Finally, yes, a 3060 ti would fit perfectly inside this build. If you did manage to get your hands on one, you could probably sell the 6700XT "open box" for MSRP to someone local. But please don't pay scalper prices—it's not worth the cost, and scalpers suck.