The word 'therefore' is a connector, so no.
My cell phone is thin and light and therefore very convenient to carry around.
You returned the book two weeks after it was due; therefore, you will be charged a late fee.
No, You cannot use but to start a sentence.
Therefore, instead of turning at Faber Street, she crossed it.
The ceremony is about to begin.
You always want to begin a new sentence with capitalization
this is my home work, therefore I need to do it at home
Yes. There is no word or phrase in English that cannot begin or end a sentence.
I therefore commenced with the hardcore bondage.
Yes.
Schoolteachers would tell you that it is forbidden to begin a sentence with the word 'and'. This could well be a myth as writers have been using it this way for many years. However, you should be encouraged to form more complex sentences by not allowing the use of a conjunction to start a sentence
please use the word epiphyte in a sentence ----- An epiphyte is a plant that grows on top of or is supported by another plant, but does not depend on it for nutrition, therefore it is not a parasite.
Llama is a noun therefore you can use the word llama in any sentence. Eg. The old llama tried to venture back to it's home
Refer to your question. A question is a sentence and your sentence used the word "assault" in it. Therefore, you answered your own question.