I wanted to build a split Ergo from scratch, with a slightly more aggressive stagger than the Lily58 style board I had previously built. I also wanted to have a stabilized 2U spacebar and some RGB. The part that was most time-consuming was definitely designing the case in CAD and getting the switches and stabilizers to fit properly. Fortunately, it's all pretty well documented so there wasn't too much trial and error involved. Overall, it turned out pretty well!
I have three different kinds of keyboards. Regular, Alice and split ergo with columnar stagger. It always takes a little while to get back to speed when I switch boards. But I think that the layouts are different enough so that a distinct muscle memory forms for each one. I guess that the most important thing is that you should be fairly proficient with touch typing on a regular board before trying a different layout. If you are still in the phase of learning, I imagine that it gets really frustrating.