No, sat is a verb - the past tense of sit.
You can begin a sentence with a verb if it is an imperative sentence but then the verb is in the base form not past.
eg Sit down! Look out. Clean up your room.
The violist sat poised and ready for her part to begin.
I unhappily stomped off to begin the essay that was due tomorrow. The cat sat unhappily in the rain.
In the sentence, You sat down: You is the pronoun subject sat is the verb down is the adverb.
Sat is the verb in that sentence.
The student sat in his desk for the whole class.
She sat quietly in the library, reading her book.
The first noun in a sentence may be the subject of the sentence, but NOT ALWAYS, for example:John sat on the bench. (the noun 'John' is the subject of the sentence)He sat on the bench. (the pronoun 'he' is the subject of the sentence, the first noun in the sentence is 'bench', the object of the preposition 'on')
Assuming you mean what would the sentence be if all nouns in the sentence The farmer wore the coat and sat on the box by the river were pluralised, then the answer is The farmers wore the coats and sat on the boxes by the rivers
I sat in a chair while watching television. Bob slowly sat down, but was still curious!
The phrase "The Cat in the Hat sat on a mat" is an example of a simple sentence in English, consisting of a subject ("The Cat in the Hat"), a verb ("sat"), and an object ("on a mat"). It showcases basic sentence structure and can be used to teach sentence formation to beginners.
Yes. There is no word that cannot begin an English sentence.
Yes, it is correct to begin a sentence with the pronoun "you," especially in informal or conversational writing. For example, "You can start by checking the top shelf for the book you're looking for."