I have no experience with AMD, but have heard positive things about here, so they may want to chime in. AMD used to be power hungry but I believe they worked on that.
Since this will be a pricey system anyway with the Titan RTX, I would suggest to go with 64 GB RAM. The motherboard should handle that.
I agree with getting 1 TB for system drive. I have 500 GB, which is OK, but 1 TB is not a waste.
For your storage drives I would go larger. Since SSDs are so much cheaper now, I would get a 2 TB for your first storage drive. I use that one exclusively for RL content and projects (so Template and Custom) and I have already over 700 GB. So 2TB (or more) will give you room to grow.
Since your second storage drive is a hard drive I would get 4 TB or more. This is where I have everything except RL content, such as downloads, images, Vegas video projects, etc. I went for a Hitachi (HGST) Ultrastar 4TB drive, which is an enterprise-level drive with 5 year warranty. But, there is some confusion as it seems that this now goes as Western Digital Gold...:unsure: