I believe you can take day trips to Arenal from San Jose.
Active night life indeed, prostitution is legal in Costa Rica.
From the composition, looks like any additions will be put in the foreground, so I can pretty much guarantee either squirrel monkeys, a quetzal bird, or both, will be appearing.
I'd go with Arenal Volcano simply because it's probably the most well known volcano attraction in Costa Rica. I doubt they would get as specific as the Arenal Observatory Lodge, but who knows.