1. For me it took about a year or so until I surpassed my QWERTY typing speed with certainty. I typed about 80-90 wpm on QWERTY and currently type at about 90-100 wpm on neo.
2. Yes, it's not a big issue. I rarely type QWERTY nowadays, but whenever I have to it clicks after a few minutes and I can type at maybe 70% the speed I typed at before. I'm certain were I to use it more, I would be able to type both at my "native" speeds. I also relearned all my emacs shortcuts pretty quickly. Using emacs is harder on QWERTY now, but fortunately I pretty much never have to do that now.
3. Due to 2, it's not really a problem. The actual problem is the other way round. You cannot easily give someone else access to your computer. It can be a bit annoying to change keyboard layouts each time someone else wants to quickly use your computer.
Hope that gives some perspective.