One person who is alone is able to make a Seder. There is no minimum number of people, although it would be nicer is you had other people at the Seder celebrating with you.
Four glasses of wine are drunk as part of the seder.
At sundown.
Seder = סדר
There are no restrictions on what may be worn to a Seder, but it is a joyous celebration, and people usually dress up.
night of passover
Four is a recurring number during the seder (for cups of wine, four questions, four children, etc), but there aren't "4 promises".
No. A Seder is a Jewish religious meal recalling the Passover.
Sometimes.
At the Seder meal we retell the story of the Exodus from Egypt.
Generally it occurs only during Passover, a Jewish holiday. There is also a seder for the holiday of Tu Bishvat, but this seder is rarely observed.
One of the foods on the Seder plate is the Z'roa - a roasted shank-bone of lamb or goat, or a chicken wing, or chicken neck. It symbolizes the korban Pesach (Pesach sacrifice), which was a lamb that was offered in the Temple in Jerusalem, then roasted and eaten as part of the meal on Seder night. See also:More abut the Seder meal
The Jewish people eat the seder meal to commemerate g-d taking them out as a nation from Egypt the land that they were slaves in for more than 200 years.