I've been to Crystal River several times, but never for longer than a day. It's a fairly good sized town, I'm pretty sure there's your standard assortment of fast food. There are several boat rental places, and a few dive shops that'll take you out for a good price. King's Spring is a beautiful dive, as long as the vis is good, but I might advise that you go out there with a shop the first day...it can be hard to find exactly if the vis is very poor. It is a large cavern with TONNES of nooks and crannies to poke around in, but be careful, there are definitely areas out of natural light, which are technically cave zone. Run a line

You'll need lights.
A google search will bring up many places to rent boats, and I've never heard anything bad about any of them. I just bring my own boat, though....
American Pro is the large dive shop there, they are alright but not the greatest. Don't expect a cave fill. They dry fill their tanks, so if you have time, go eat lunch and pick them up later, and make sure to request they top them off when you return to pick them up. I have had issues with short fills on my HP aluminum 100s.
Also, it is manatee season. There are slower and mor estrict speed limits in place, and for good reason. Manatees can be anywhere and everywhere. Please, please, please boat slowly and responsibly!! Also, if you are not an experienced boater, and are renting a boat, and will be leaving it alone, I suggest you read up on how to anchor a boat correctly. I would also advise that you go to Walmart and get a second anchor and line, so you can employ some of the double anchor techniques. Get a marine map of the area, and know the tides! Also, wear polarized sunglasses, they will help you see manatees in the water. The rule of thumb is go slowly!!
