I'm no expert, but we planted our bed this year. Most places wanted to sell at least 25 crowns which is what we got. We planted the crowns about a foot or so apart. The spacing is related to how big the asparagus you harvest will be. As I understand it, we will be able to harvest lightly for 2 weeks next year and more each following year as the plants establish. The unharvested spears turn into feathery plants that are attractive. Nobody realizes it's asparagus until we tell them. We've found the plants benefit from a little support so they don't flop.

The crowns we got were from Johnny's, I think. They like a lot of compost, so we've been layering it on. So far no problems and I'm looking forward to next Spring. We planted the crowns in early May.

I had an asparagus bed a long time ago, until "someone" parked a car on/in it.
Anyway. I remember the man at Agway telling me to buy male plants because they don't set seed.