Do these light up like Dinoflagella?

Not that I have witnessed, but maybe under the right (very rare if possible) conditions they could.

Will I bee able to see these creatures under a microscope?

That would depend of how good a microscope you have. These are 1 celled plants (algae)

Any suggestion on how much to dose smaller tanks, such as those holding brine shrimp?

I use this to feed to my copepods and baby brine shrimp cultures that I feed to my dwarf seahorses. Each are contained in about 2 quarts of water, and I dose the water betw 2-4ml daily or until the water is a tea colour. Here's what Mercer of Montana suggests: "The daily addition of 2-3ml to every 40 gallons of saltwater in your system, pouring directly into the display tank, or associated sump (the cap on this bottle will hold approximately .5 oz). Protein skimmer should be turned off during this time, to allow more of your phytoplankton to be absorbed by your livestock." I believe that's for feeding anemones, etc. in a "reef" tank.

I have 150 Gall of water, will this 8oz last for a month?

It will last for over a month if you put it in your sump. If you put it in your main tank during the middle of the day light you might not have much luck. If you do it with the lights off they might have a chance. Depends upon the availability of places to hide.