Photo...wow, you sound a lot like me before I gave it all up and moved down here for good. I was working at a newspaper as a photographer/reporter and doing sports photography freelance for various organizations. Now, I live here with my wife of 6 years, run a transport business and have never been happier.
There are a TON of great places for photos in Costa Rica. The biggest problem is the security issue. You would NOT want to walk around San Jose (or 90% of the rest of the country) with thousands of dollars in equipment without some kind of security. When I see professional photographers doing, for example, a fashion shoot in Parque Espana, they had a three-person photography team (camera and two light guys) then several security guards.
If you can keep you equipment hidden then you can get away with a bit more. I used to put my camera in the Canon bag then put that inside a large red duffel bag so no way to know what I had in it. When I'd see a shot I wanted, I'd check out the surroundings and if I felt comfortable, I'd pull out the camera and get my shot and then repack it.
Now out in the country, it is a bit easier. A lot of great places for photography will be tourist areas where most of the people are tourists along with the usual compliment of 'tourist police' that hang around these areas. For example, I feel safe using my good camera on the Tarcoles River Bridge to photograph the crocks. There are also a LOT of great places for pictures where there just isn't anyone else around. Only problem with this kind of photography is you will need transportation/driver/guide so an added expense.
As for places to shoot, here is a (short) list:
1) Volcano Irazu/Turrialba - These two volcanoes sit next to each other. Irazu is not real active right now, just some occasional steam/ash. However, Turrialba is very active, belching out lots of smoke/ash. Neat thing is, you can photograph Turrialba from the summit of Irazu which is over 11K feet up. It is also one of the only places in the world where you can see both the Atlantic and Pacific oceans at the same time. Only caveat is during rainy season, the weather usually puts the summit under cloud very early in the day so a very early start is mandatory.
2) Volcano Poas - This volcano has a better crater than the others and also has a second crater with a beautiful lake. The drive up and down have incredible views of the Central Valley. You can also go over to La Paz waterfalls in the same trip.
3) For wildlife, I'd suggest the La Selva biological preserve. Some rare birds, monkeys, sloths and a lot more are everywhere.
4) Volcano Arenal is also a great area for photography. The volcano has started shooting out ash/steam in the last few weeks but nothing like it used to, with the incredible lava shoots you see around the internet. There is also a ton of wildlife, a beautiful lake and the drive up/back is one of the most scenic in the country. There is also a tour called the Cano Negro Wildlife Refuge tour where you will see more wildlife than you can imagine.
http://www.arenal.net/tour/Cano-Negro-w ... refuge.htm5) For the perfect beach photography, Manuel Antonio is the ultimate spot. Incredible beaches, great hiking trails to some very scenic places and a ton of wildlife.
6) For a compromise location for chicas/beach/wildlife, I'd recommend basing yourself out of Jaco. Great chicas at night and a ton of good photo ops in the area. Manuel Antonio is just down the road, Tarcoles Bridge is on the way and access to all the adventure activities you can imagine, many of which will provide great photo ops.
Obviously, you will need transport to all these locations. I would NOT recommend a bus if you are carrying the kind of equipment I assume you will. Private transport with a reliable driver would be my recommendations and I can certainly help you out with that.

On what to bring, I'd say if you are serious about wildlife/nature photography, your best camera along with your longest lens for wildlife shots, a short lens for landscapes/panoramas and a good zoom, like my Canon 70-200L (4.0) for generic stuff. If you shoot with Canon and hire me for transport/security I have no problem letting you borrow either that lens or my 28-135 IS lens. I'd say leave all the other lenses at home. On lights, leave that all at home and bring your best on-camera flash. If you have one that can remote trigger and maybe even a small reflector for it, even better.
On chica photography, most don't mind a couple of clothed shots before you start a session. If you want to do a whole photo shoot with a girl it will be more difficult. Many will not want nude pictures taken at all. Others will ask for more money for a few nudes. No idea what they might ask if you want a full photo shoot so that will be an experience for you. If you don't speak any Spanish, that might also be a problem trying to direct the girl. For simplicity, not sure I'd try for full photo shoots with the girls unless you do speak Spanish or have someone there that can help with directions and bargaining for her time/photos.
I have a photo gallery of some of the shots I've taken on my website if you want to check it out (
http://www.puravidatransport.com/photos.htm). There is also some basic info about various places to visit with links to more photos I've taken of those individual locations (
http://www.puravidatransport.com/advice.htm).
Hope you have a GREAT trip and if I can be of service, answer any questions or anything else I can do to help make your trip a success, just e-mail me or PM me here.
Steve