Option #1. fastest,easiest way is the Turnpike all the way to I-595 and go east.
Option #2. Turnpike to the Ft.Pierce exit (exit 152 on the turnpike) and grab I-95. Pros: You'll save like $8-$9 in tolls. Cons: I-95 has more traffic
Option #3. You mention taking a coastal route,taking US1 and A1A the whole way might take you 8 hours or more and A1A is not a straight shot the whole way it,you'll have to get on US 1 at times.If you want to take this route the whole way then from Orlando take the 528 Beachline expwy towards Cape Canaveral and take A1A south.
Option #4. Take a coastal route only part of the way.Take the Turnpike to the Ft.Pierce exit and then get on 95 until West Palm Beach (Okeechobee Blvd.) and from there take the A1A south,instead of being a 9 hour trip It'll be 5-6.