Most advice is to NOT introduce the kids very early. Let the relationship develop and your kids ARE your priority, you can't change that.
Most of the time, people say "coupledom" when it becomes intimate, but that is up to you both. That is my line, when sex starts, we are a couple. I have that discussion early, so the guy knows what to expect.
As a full-time single Mom, I have to schedule my dates well in advance and the guy just has to get used to that…it is what it is.