They are used interchangeably, but they also have a subtle difference. "I" is more of a directional marker, as you'll see it in other sentences that don't necessarily talk about physical locations, like "Nānā i ke kumu," translated as "Look to the teacher." "Ma" is used more to describe where a subject is at physically, in the bedroom, on the table, in Honolulu, etc.
Excuse the correction, nouns with descriptions have their adjectives placed after the noun, such as "ke keiki hūhū" meaning "the angry child."
For your English sentences above, those are particular sentence structures known to some as Stative Verb Sentences, describing the state something or someone is in. They have the structure 'Discriptor + Subject'. So "The man is happy," meaning the man is in a state of happiness, translates to "Hauʻoli ke kāne." And to turn that statement into a question you would simple add a question mark, like you said, "Is the man happy?" == "Hauʻoli (ʻanei) ke kāne?" The "ʻanei" word is optional but is specifically used to emphasize that it is a yes/no question.
Take my ʻike with a grain of salt as I attempt to give constructive criticism. ʻAʻohe pau ka ʻike i ka hālau hoʻokahi. =)
Hawaiian questions are similar to English, where it can be a statement with a raised inflection at the end of the sentence. In writing, simply end it with a question mark. "Aia ʻo ia ma ka lumi moe?" "ʻAe. Aia ʻo ia ma ka lumi moe." Is she in the bedroom? Yes. She is in the bedroom."