No a sedan is fine. I usually prefer to rent a small AWD SUV, even a Diuhatsu Terrios is fine (Toyota Emerging market brand), but a Toyota Rav 4 or Susuki Vitara is fine too...I just like to sit up higher and the sight lines are nice.
It will be all two lane roads, other than the Toll/Caldera from Alajuela to Jaco...
All the roads are surfaced, no worries there. Getting from MA to Orosi will be a lot of driving, but once on others side of San Jose/Cartago, a easy and gorgeous drive....
I use Alamo and Mapache. I get all the insurance, makes a small SUV about $60 day but you still have to give them a $1000 Deposit Hold on the CC...
Don't drive at night, gets dark 530-6pm...unless just down road to dinner...
Any reason you have not considered the Osa, or La Amistad/Talamanca area? Or even Tenerio/Rincon areas...
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