I'm constantly amazed at people who say they have a xxx megapixel camera and then shoot jpegs. You are in effect giving your camera permission to throw out about half of the detail in the photo before you download it. It will discard detail like blown highlights or dark shadows that are easily recoverable in the raw image. It's worth shooting RAW if only to adjust the white balance in post processing.
JPG-FINE is not the best quality that your camera is capable of. Compare the file sizes between RAW and jpeg. The difference is the detail.

I have what I think is the lens you used and I love it, and could afford it, but I rarely try and use it wide open. (My avatar was shot with this lens.)
However, don't confuse art photography with commercial photography. Two different genres for two different uses.
Your images don't have sufficient dof for stock photos. I agree with gessman about getting the whole face in focus.
I use stock photos and wouldn't buy them even if they were the right images for my work.
Starting with a low ISO is good, but these days "low" can be 200 or even 400 if you're hand holding.
Shutterstock was right. Learn from it if you want to submit more images. It's not a big leap from good to just right.
Good luck with it!

Thanks tdekany - non-issue is good!

Since some of you have obviously delved into the 4/3 world, just one question. Maybe it sounds silly, but I think it could be a problem.
Many 4/3rds have touch screens. I'm particularly interested in the OM-D E-M5. Some of the reviews say that even turning off the shutter option on the touch screen it's easy to turn it back on accidentally.
Given that I always use the viewfinder, am I likely to take a photo (or change settings) with my nose?

How are you shooting your HDR sequence? Are you using exposure bracketing? Are you using a wireless remote? I'm a bit puzzled about how the focus changes between shots.

See ... not so silly at all!
Google neutral density filters for a better explanation than I could come up with - also handy if you do landscape photography in bright light.

Don't be so mean guys - we've all been seduced by a bargain.
The hood is to cut lens flare - that is light (generally sunlight) coming in to the lens from close to the front. It sends white streaks across your photo. If you shoot a lot in full sunlight they're handy, but if you're stuck you can always shade the lens with your hand.
The problem you have with just buying a lens hood (as someone has mentioned) is that it has to fit the lens. I have two mid-range Canon zoom lenses - the filters are interchangeable but the hoods are not. Line up the dots on the hood and the lens and see if you can twist it on easily. If not, it's probably not for that lens, which leaves you in a difficult position because you don't really know what lens it suits.
Regarding the filters (assuming they are the right size for your lens), the polarising filter is great if you're shooting landscapes. The others could be anything. The "outdoor" one could be a neutral density filter, no idea what the "indoor" one could be. Might need better descriptions. What colour are they? How transparent do they look. One might just be a UV filter - mainly useful for protecting the front of the lens.
I admire your spirit. Happy shooting.

I've had the banding problem occasionally for no apparent reason - just a processing glitch which is annoying but as I generally take more than one shot of the same scene, not too serious. The superimposed shots are new to me!
I agree with the suggestion that you should format your cards rather than just delete the photos - this should pick up bad sectors. However ... this is an old card. Any memory device becomes less reliable over time, and cards are subjected to stresses that the HDD on your computer will probably never experience. You could replace it very cheaply - cards are cheaper, higher capacity and much faster than they were when you got this one.
Functionally there's no difference between CF and SD cards.

Just to return to the original question. Yes that is correct. Dividing the card size by the size of the photos will tell you how many (of that size) it will hold. No magic.

However ... bear in mind that your RAW files will vary in size a bit, and like any computer drive it can crash, so getting your files off your card and backing up is always a good plan!

If you shoot with the sun behind the photographer your subjects will just squint. Try and place the sun behind the subjects, but not directly behind them or you will probably get lens flare. If you get the sun onto their heads slightly to the side, you get a nice effect. Yes you do need fill flash or a reflector - get one of the very cheap fold-up reflectors that give you the option to use white, gold or silver. White or silver will look more natural in daylight. You'll need someone to hold it for you. Try using the silver or gold side to get the angle right, and then turn to the white side for a more subtle effect.