A typical first timer visit to CR which would include an active volcano, Cloud Forest, rain forest, beach would be, Fortuna (Arenal Volcano), Monteverde (cloud forest), Manuel Antonio (quepos). These places would be pretty much finished with the rainy season by the end of Nov. It lasts a little longer the further south you go (Osa). The Osa is my favorite place but it is difficult to get to. Flying is the quickest. Pearl of the Osa is a reasonably priced place to stay just outside of Pto Jimenez.
Regarding transportation. Depends on your budget, lots of options. Fantasy Bus and Interbus are around $25 per trip. Local buses are pretty good and very inexpensive. Monteverdeinfo.com has a bus schedule.
Getting to Monteverde from Arenal can be done one of 3 ways. One is by bus/car (5hrs). One is by jeep/boat/jeep where you take a 4x4 jeep and then a boat across lake Arenal and then another 4x4 up through the mountain (3hrs) and the last option would be by horse (3hrs).
Any time you are in the mountains it can rain or be cool and windy. Monteverde can be anywhere from 55 degrees to about 75 degrees. Up there it can be raining in the cloud forest but dry as dust in the town. Taxis most places in CR are pretty plentiful and not terribly expensive.