No, You cannot use but to start a sentence.
The ceremony is about to begin.
You always want to begin a new sentence with capitalization
Yes. There is no word or phrase in English that cannot begin or end a sentence.
Condescension is a long word and i am putting it in to a sentence.
antidisestablishmentarism is a very long word.
Example sentence - We walked quietly in the long hallway.
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
That area will be radioactive for a long, long time.
for example "how long is a metre?"
The immunization was long and painful.
there was a tsunami in japan not to long ago
Example sentence - He had no idea how long it would be before the crime was discovered.