"A small port"
Translation:En liten havn
Not in American English. Maybe in British English, though I'm not familiar with that usage. Typically, the term "gate," refers to an entry/exit built into freestanding walls or a fence (a fenced property), rather than an entry into a building. You may be thinking of the word "portal," which means (dictionary definition): door, entrance; especially a grand or imposing one/a large door or gate to a building (such as a church)"
It works like all other adjectives in that it has to agree with the gender and number of the noun, its only irregularity is that the plural form looks so different to the singular forms.
The singular indefinite form depends on the gender:
en liten jente (m)
ei lita jente (f)
et lite barn (n)
The singular definite form is either "lille" or "vesle" depending on the dialect, with the former being the most common.
The plural form is "små" across the board; små jenter, små gutter, små barn.
I'm afraid not, as "small" and "little" are technically interchangeable when you're speaking of size.
"A small/little house"
"Et lite hus"
"Several small/little houses"
"Flere små hus"
When you're using "a little (bit)" to speak about the degree of something, then it will be translated with "litt":
"This is a little confusing."
"Dette er litt forvirrende.