it depends how big the plane is
small = 500lb ish
big = 10s of tonnes
Let us say that we have an empty airplane that weighs 3400 pounds. It is going to carry 30 passengers, who have an average weight of 180 pounds per passenger, and each passenger is also going to carry an additional 20 pounds of luggage. What will the airplane weigh with all passengers and luggage aboard?
All different aircraft carry different weights. For instance a Cessna 152 may carry about 500 pounds all up, whereas a Boeing 747 may carry over 500,000 pounds including fuel and cargo.
2 at a time
The a380 can carry up to approximately 853 people
Depends on its design limits.
You need a license to carry a firearm in many places. You cannot carry one on an airplane.
Depends on the airplane. Some really small ones carry only the pilot but some of the really large wide bodies can carry as many as 300.
About 23 US gallons
0 to hundreds -depending on the model
40000 POUNDS
no
Those seagulls would weigh two pounds whether they were sitting in the airplane or flying in it. This is because they have push the air below them (in the airplane) down with two pounds of force to keep two pounds in the air. So, yes, the seagulls would add 2000 pounds to the airplane's weight.