Well for starters you did well, however I hope you did not rent (book) a car for the entire period (a few months you said?), unless you got a good transferable deal from your home country. Rentals in Accra are pretty hefty, because there is no credit system and shady or non existent auto insurance, for which reason you almost have to buy the car and get a refund upon its return in perfect condition (a bit exaggerated to get point across). Rent (book) on a need to basis. Since you've initiated most of your arrangements already, I'd just ask you to enjoy Ghana objectively, what's too good to be true is indeed untrue, what your eyes can't believe, it's against the law, everybody gets away with it. Oh by the way always make sure you dictate to your driver what speed limits you want them to maintain at ALL times. For your trips start with the coast.
Visit- Soak up enough of Accra, then Ada, Akosombo(ride the lake), Shai Hills(magnificent), Ada, Aburi Mountains(the ambient air). Try a few waterfalls mid-Ghana and Northern wildlife reserves. Most other things are overrated, but I am sure somebody will convince or force the issue. Return to Accra and soak up a little more where you left off. Again have fun, I love Ghana the way I know it.
