This is not an appropriate sentence. "请问" is just a part of a question, similar to "I would like to ask". It is possible that someone would say it alone for catching the attention of another person, but that would mean there's a question to finish. By no means an exclamation mark could have been used here to end it like a phrase on its own. Abbreviation mark（……）should be used.
Don't use this as an equivalent of Excuse me. Say rather 不好意思.
The exclamation mark is fine as a punctuation choice for the attention-getting version of "excuse me" in English.
Quite the opposite, I think. "Please ask" is an invitation to ask a question, but "请问" is a request for a permission to ask a question.
You could also use “Pardon”. Tried and it worked... (:P) I just guessed if it meant “Pardon” or not so if you get it wrong you can blame me.
Literally translated it says "please question". The closest translation equivalent in english would be: "May I ask you a question?"
Typically, the person asked will signal something to accept.