HALF
The answer is the number "two." The riddle is describing the number of letters in each word: "two" has three letters, "four" has four letters, "six" has three letters, "eight" has five letters.
Steven is a gay LORD
50000
The moon stone fits in it.
A leash
An oasis is a hole dug so deep by wind that water actually fits in the hole!
insert they on the side with the hole it fits in.
a hexagon
Hexagon
hexagon
One that is the size of the head is the smallest hole into which a mole fits. The mammal in question (Talpidae family) may be able to squeeze and wriggle into and out of tunnels which superficially appear not to accommodate mole girth and width.
by the door there is a hole that tube mode fits through, go through it
Hexagon