Yes you can. Example:
Okay, I will go with you.
Yes.
okay
Sure. Am I wrong? That is an example. Am I interrupting something? That is another. Well, that is not strictly true, that is starting a question with 'Am', okay a question is a type of sentence. But you cannot start a statement with 'Am', the word should be spelt I'm.
Yes.
It's okay for you to stay.Yes as in For example, .... and For once in your life, do the right thing.
can you start a sentence using the word phishing?
Okay, this is my drabbest shirt.
okay here is a sentence: "I don't know what prognostication means!"
Yes, it is OK. Example sentence: On the day of the race, I woke with a bad headache.
Yes, if the sentence is otherwise well written and it fits within the context of the paragraph.
no!
No, you cannot start a sentence with "no" unless you need to do so. No reason exists not to start a sentence with that word, as you can see. No one will care if you do start a sentence with it.