For informational purpose only - opinionated too.
The road really isn't all that bad these days. I was on it in February.
Jaco is the only place with any working girl to my knowledge and it is what it is... just a little town.
It is hot, but as long as you are mentally prepared for the hot, it shouldn't be too bad (not like 95 degrees will be a surprise, like oh crap!). The good thing is that the beer goes down really easy, tastes good too.
I'd go for 2 night myself - if you leave really early in the morning after the second night you'll get to SJ just in time to check in, shower, get something to eat, go enjoy yourself.
SJ is okay, but you can't be doing girls all day every day. When I walk the streets in SJ, it is just another city so nothing special. Jaco - well at least they have some bars that are looking out at the ocean and so the atmosphere is just perfect in my opinion.
Try Clita's (spelling?) - on the beach at the far end of town.... near the Best Western. Ask and someone will give you directions - nice casual place with some nice non-working girl barmaids.
Good luck - everyone has their preferences.