Well, I really do NOT like the selective color. In the first image it makes no sense at all. It draws your eye to....what? The image should be about the firefighter's eyes - the concentration on the face. All of which is lost by drawing attention to stripes.
The red bucket shot is not as bad, but I still do not see how it improves the image. To me, that is about the people - not buckets.
Same with image #3. If they yellow guy is the subject, I am not sure why.
Your boudoir work is wonderful - this is not up to your ability.
Just because you can, does not mean you should.
I noticed right away that the clouds were added. The clouds have a late day sun from the left, your main image has an earlier sun from the right. When you composite an image, the lighting has to match. Take lots of sky images to use in a composite and then use the ones that match time-of-day of the main image. You can always flip the image to match if needed. But mid-day clouds and a sunset subject will never work. :-)
If you shoot RAW, it does not matter what your color space is set to on the camera as the file contains all the colors the sensor is capable of capturing. The conversion to a color space occurs when your process the file in Camera Raw or Lightroom. In Camera Raw, that choice is made at the bottom of the display where it shows color space, bit depth, pixel dimension, and PPI. All that occurs the moment you open the file from ACR. You can click on that to change how the file will be output to Photoshop.
In Photoshop, you can tell what color space you have down in the lower left of the image display - it is one of the choices under the little right-pointing triangles.
Remember you can never go "up" in color space - once it is sRGB, converting to Adobe RGB is worthless - you have already lost the colors from Adobe (or ProPhoto).
Most labs require sRGB. If you print on most recent Epson/Canon/HP printers, you can send an AdobeRGB file. Heck, some of them allow sending a 16-bit file!
IMO, the difference between sRGB and the others is not all that great. You do lose some of the highly-saturated greens, oranges, blues,etc, but skin tones are all within sRGB and I am a portrait photographer. I shoot RAW, but convert to sRGB.
Not be be a wet blanket here, but check your state laws - in most states it is illegal to trespass on the railroad right-of-way. Photographers have been fined.
Even abandoned tracks are probably still private property. The railroads see it as a liability. Should you (or a client) get hurt, they see a lawsuit coming.
If this is a class assignment, I would question if the instructor knows the local laws. It might not be a big deal - it might be exposing his students to legal action!
OH - I like the first one.
I hope you can recover your images, but for future reference, your D7000 has TWO card slots and can be set to use the second slot as backup. The chance of two cards failing is pretty remote. Use it - you paid for that feature!
Usually, color blindness is in specific parts of the spectrum. I believe one of the more common types is the inability to tell the difference between red and green.
There is also a blue-yellow blindness. Guess you would never see a cub scout :-)
But it is not a case of seeing just grays.
Better you should be a piano player in a brothel. Better pay and shorter hours.
The backgrounds have been mentioned - and for good reason. Remember this: the background is JUST as important as the subject. If you are just shooting family snapshots, this is not a big deal as those images serve their intended purpose. But if you want to shoot more portrait-like images, then the background is critical. In the three images you posted, the BG is awful for a portrait, fine for a snapshot. Does that make sense?
The one that fawlty128 re-did is an improvement, but now it is a mixed-key image...high-key background and low-key subject. Better than the original, but still not what you want.
fstop22 is right on the money. ANY DSLR out there now will do what you asked.
Lens choice is more important. The literal answer to your question "...the best..." puts you up over $40,000.00 or so. You can spend 1% of that to get good landscape images.
Be careful of teleconverters. Many Nikon lenses will not accept them at all and as has been mentioned, unless you are starting with a constant 2.8 lens (or faster), you will find the light loss might well make autofocus difficult or impossible. Any effective aperture darker than f5.6 can kill AF.
IMO most TCs not made by the lens maker can be iffy at best. Very few 2X converters are really sharp. The Nikon 1.4 and 1.7 are amazingly good - the 2X just so-so. Some of the Kenko converters have gotten decent reviews.
See this:
http://www.digiscoped.com/teleconverters.html BE SURE to verify that a converter will work with a given lens.
Gizzy. That is why it is often called grayscale - or monochrome.
These are VERY nice. I the one where she is kneeling (the black lingerie) I would clone out or crop out that tiny bit of black in the lower left corner. Very well don.
OH - Sman reminds me of the Saturday Night Live character that Dana Carvey played - The Church Lady. Watching him go nuts has been most entertaining.