I've been down to Spanish Wells twice now. Both times it was March. We stayed at the Adventurer's Resort. A nice place and quite inexpensive. We also rented a boat from them. It turned out to be the owner's boat. We've stayed in touch with the woman who manages the place, so if you need a place to stay, I could send her a note for you.
What do you want to go after? We primarily went for bones, but when they weren't around (which seems to happen quite often in March) we had fun jigging for 'cudas in the mangroves. We also didn't use a guide ourselves, but there were a few around. We thought we would do as you plan on our first trip, but we ended up just going to one of the nearby flats the first afternoon and having some luck, so we never did hire one. One of the guides that is around is a real character. His name is A1 Broadshed. A1 is his first name: a buddy got a card from him! I don't know that he guides for bones, but he does take people out to the reef areas to fish. "No fish, no pay" is his motto.
I think it is best to have a boat. There is one nice sand flat at the north end of the island and a turtle grass flat at the south end which can be reached without a boat, but that is about it. We liked a large flat near the ferry from North Eleuthera on the North Eleuthera side of the ferry. There is also an amazing area called Corrie Sound a little ways down the coast of Eleuthera. It is a completely sheltered sound, just spectacular. The other islands near Spanish Wells have flats around them as well.
That's just some general stuff. Do you have any other specific questions?
Juro: the 10wt line was great. It matched the Reddington 990 nti nicely. I will get the next story together too. I haven't forgotten :-)