That should all work fine. Inevitably, there is some effect, with one card, on the other, but the Gigabytes are not particularly thick, you have 3 slot spacing, on that board, plus, I believe, that case has side fans, so the effect will be minimal.
There is no point to 16GB of RAM, for gaming. Some Autocad processes can be memory demanding, especially in 3D, so it could be worth it, for that. If you use 2x8GB, to same spec, it won't have any detremental effect.