I agree with most of the above. If you're going to be in Arenal and Papagayo, I'd suggest skipping Manuel Antonio. I've been there many times but it's a long drive to and from for a trip like yours, and the park is overrated. It has some nice beaches, but you'll get that at Papagayo. The animal life around Arenal is about as good as MA. Make sure to do a Canopy Tour (zip line) near Arenal for some fun and the best views of the area. The drive around Lake Arenal on the paved roads is nice.

I highly recommend going to La Paz Waterfall gardens the day before your departure, along with a trip to Poas Volcano. Yes, LaPaz is for tourists, but it's very well done. You'll probably enjoy it more than MA, given the other places you're going, and you can stay close to the airport when you do that trip. Poas is the prettiest volcano in CR, but try to go their before 11am because it often gets cloudy after then. If you stay in a nice place near the airport (Hampton?), your hotel can probably arrange this day trip with some advance notice.

I think Monteverde is very nice. The last hour getting there is on a bad road, but it's okay, even without 4wd-big buses do it. I recommend Selvadura as the best place to spend a day. It has the best butterfly garden, humming bird garden, canopy tour, and suspension bridge walk. There are other little things to do around Monteverde for parts of another day.

With the exception of the last part of the road to Monteverde, the roads you'll be on are fine.

Do not attempt to drive in the San Jose area. The lack of signage and road names, and crazy drivers will make it a rough time for anyone not familiar with that arena.