In addition to the scope and camera you will need two linear polarizing filters.
If you take the two filters and look at a light source while rotating one filter,
You will see the light darken and lighten as you rotate. You will use the
dark position (crossed polarized light). If you place a birefringent material
between the filters you will now see colors. You can place the filters anywhere
in the optical path, as long as the specimen is between them.
You can use almost any microscope. You will need planar (plan)objectives.
This means that if the center of the image is in focus the whole image is.
You can get a new LOMO scope with excellent optics,for under $500 on Ebay.
American made Reichert or AO scopes with superb plan achromat objectives are selling
as low as $300 on Ebay. Used research grade Leitz and Nikon scopes go for under
$1000 on ebay. You can buy adaptors to mate the scope to the camera on Ebay.
If you have a coolpix, you can get by without an adaptor. The 28 mm
filter thread on a coolpix will mate directly to some Leitz scope eyepieces
and will be the same diameter as most standard (23 mm tube) eyepieces.
You want a wide field, high point eyepiece.
Here the Coolpix camera is held at the correct position by a tripod,
without an adaptor. The head on this camera swivels, which is a great feature
for microscope and telescope photography. Additionally the extreme macro
capabilities of the Coolpix make it the camera of choice for microscope
I am not a microscopy expert, so I wont answer microscope questions.
A great article is at: http://www.microimaging.ca/microscopy.pdf