Minor Greek gods and goddesses had no major followers or cults during the period the Greek god and goddesses were recounted to "classic" mythology.
There were 12 main gods, such as Zeus, Poseidon, Aphrodite and Hermes but there were loads of minor gods, unfortunately i don't know the names of any greek minor gods :( Hope this helps you :D
Greek or Romans ?
both
A lot. The Greeks worship many gods and goddesses so you can't find the exact number. There are many major and minor Greek gods and goddesses. You have to be more specific, how many Greek major gods or how many minor gods.
12 olympians, hundreds of minor gods
athenaartemisapollodemeterherahestiazeusposeidonhadesdionysuspannikemorpheushecatehypnosboreaszephyrosaeolusnotoshermesjanusjanuamphitriteaphroditeerosareshephaestusmercuryplutopomponatritonminervavenusneptunevulcanhebepersephoneproserpinaheliosdelphineus
The difference is quite simple. "Olympians" in reference to gods are the greek gods with thrones on Olympus. "Greek Gods" is used in reference to the Olympians and minor gods.
There are twelve main gods and goddesses(the Olympians), but there are lots of other minor gods and goddesses in Greek mythology.
Well Ive only heard of 3 Greek gods named Coronis , Chiron, and Asclepics
In Greek myth, yes.
Janus is a Roman god, and not minor to the minds of ancient Romans.
Zeus was the king of the Greek gods, so I guess he would be considered the "master" of them as well.