I've heard "bitte schön?" as a question by waiters, meaning, can I help you? Not "ja, bitte?" though. Though this article seems to indicate you could just say bitte that way: http://german.about.com/od/vocabularytips/a/The-Many-Meanings-Of-Bitte.htm But then it wouldn't mean "Yes, please"...
There should be no question mark following this. As in English, it is not being asked as a question but more as the answer to a question. The correct version is "Yes Please" or just "Please" means, "please do" or if you can do it, then do it. For example 1) Question: "Would you like a bag for your groceries today sir?" to which you Answer: "Please".
"Please" should always be followed by a question mark since you're asking for a favor to someone else - in Portuguese it is very clear: "Pode me ajudar, POR FAVOR?" = "Can you help me, PLEASE?".
Unless it has an imperative connotation (i.e., commands or requests; for example: "Please, remove the device from your computer"), I don't see any reason to not use an question mark (by the way, I think it makes the sentence more polite).
But it's simply not correct in English to say "Yes, please?" The word "please" is short for "If you please" (i.e. "if it's not too much trouble", which is also something you might say in English - and that doesn't have a question mark either.) In Shakespeare's time, a common phrase was "An it please you" which means "If you please." Modern French still uses the full phrase "s'il vous plaît" routinely; "Yes, if you please" is still used in English, but it's so formal it's more likely to be used in a joking way. I think it's more likely to turn up in British English.
Note: "Could I have some bread, please?" has a question mark because the sentence is a question, and "please" is only used as an adverb. Your example in Portugese appears to have the same sentence form, although I don't know Portugese.
Yeah, you're right. But I think that a look at this may help us:
Let me know what you think about it (even if you already saw this).
PS: I'm brazilian, so I think that my comparisons between Portuguese and English/German are not the most indicated way to enlighten the question.