My crew and I did this trip several years ago. Here's the link to my trip report: Antigua Sailing. We used Horizon as well -- they were terrific.

I don't recall having any major difficulties navigating around the reefs -- just the usual cautions. But if you're worried, get some reassurance at your chart briefing.

I will say that Barbuda was a highlight of the trip. We spent several nights there, largely having the anchorage to ourselves. Knowing what I know now, I would have been content to split the trip between Barbuda and English Harbour. The contrast between wild nature and history was amazing.

I realize now that it's been quite a while since we went, but unless things have changed in a big way, I found Antigua was not particularly friendly, and certainly not very inviting to sailors (which is ironic, since it bills itself as quite the seafaring destination). Restaurants accessible from the shore are mediocre at best (you will be happier feeding yourselves), and few places have dinghy docks for you to land comfortably. I was glad to have made the trip, but would not do it again.