I live and sail mostly in Panama City. Have sailed to Port St Joe (St Joseph's Bay) many times. Have not been to the state park in many years, but I do remember comments several years ago about the launch there being shallow. St Joe Bay is big and mostly shallow, plenty of room to anchor. There is a public ramp in downtown Port St Joe that is big and very good, so lots of power boaters. There is a city marina which is very nice, has fuel and pump out, and spaces for overnight and daily rental, with power. There is a new boat storage north of Hwy 98 bridge, on the west side, not sure what facilitiies that they have. Port St Joe Bay has a big opening to the Gulf, therefore can be rough in bad weather close to the pass.
Might I suggest you look at Panama City, deeper water, better anchorages. Lots of boats will spend the weekends anchored up behind Shell Island, a barrier island that has lots of sand beach to walk, play, swim. There is St Andrew State Park where you can launch (very busy), also the downtown City Marina has very good ramp = lots of power boaters.
Suggest you go to website below. Claiborne Young's Cruising Guides and get the one for "Northern Gulf Coast". He does a very good job of detailing the "Panhandle" of Florida. The website says that it is "out of date" due to storm damage, that does not apply to the area from Carrabelle to Pensacola, the area that you are looking at.
http://www.cruisingguide.com/cp/Scripts/prodList.asp?idCategory=22
Since you live in Birmingham, you should know, NEVER come to Florida without plenty of "bug spray".
Good luck, hope you have a pleasent "spring break".
Bill