Together, the five US states that border the Gulf of Mexico have 1,632 miles of general coastline according to a published abstract from the U.S. Census Bureau, Statistical Abstract of the United States: 2011. This does not take into account all areas of land in those states that are part of the tidal area. I could not find the statistics on tidal areas for just the gulf side of Florida.
Also, according to the United Census Bureau, the Gulf Coast is the fastest growing coastal region in the United States despite more than 13 major hurricanes that have struck the region since 2004 causing billions of dollars of property damage. About 94.7 million people, or about 29.1% of the total U.S. population lived in areas vulnerable to the ravages of seasonal storms and hurricanes. Below is a table that lists all of the counties for each of the 5 gulf coast states that touch the coast and their estimated population as of 2016. I was surprised to see that the Texas gulf coast actually has a larger total population than the Florida gulf coast even though it has fewer miles of actual coastline.