Only if its plural, like conclusions.
"In conclusion"
In your case, the question is, can a sentence come to a conclusion. Try again.
No
NO
Yes.
you can start a senetence with or but it wont be proper grammer.
Yes, sure.
You did a proper job of it.
It's perfectly fine to start a sentence with likewise, just make sure you have a comma after it.
a conclusion sentence is a sentence that concludes either a letter, peice or a story.
No it won't, unless it is at the start of a sentence.
There are many ways you could state a conclusion. Many people start concluding paragraphs with the sentence starter "In conclusion".