I'd get rid of the lure asap. I usually lure just a couple times so Juno gets the motion, and then the lure is gone and its just a hand signal. Ill go back to using a lure if she's not following the empty hand but usually it's not necessary.
As far as how long to get verbal only -again depends on the dog and IME, the trick. How I do it is I say the command, wait a second, and then use the hand signal. It's important to make a distinct separation between the two, so don't say the command and use the hand signal at the same time. Eventually, when you say "down" she'll do it because she is anticipating that the hand signal will follow. And then you jackpot!
And you can technically train as many new things as you want as long as she doesn't get confused. I'm always starting.g multiple new things at the same time.
Hope that helps!