I'm still learning so I might be missing a word, but I think "is it your boat" would be "a bheil an bàta agad". Literally, the "an" means "the" but in this case it's closer to saying (a bheil) is (an bàta) that boat (agad) at you/yours? You need the "an" to specify that you mean a particular boat rather than just a rhetorical one.
Yep! It can be a bit unusual for non-native speakers when they first encounter Gaelic, but questions follow a falling intonation pattern. The thing with Gaelic is that you don't need to rely on stress placement to tell you if a sentence is a question or not - the first few words of the sentence tell you that it is. For example, if a sentence starts with A bheil... (as in the above example), then it will always be a question.
Here's an article that explains it in a little more detail:
This speaker talked fast, some go fast and some slow. It's intended to help you learn to recognize actual speech if you hear it. Different people have different dialects and personal speech patterns. You have to just get used to it.
Also, the "slow speed" will not ever be fixed. It can only be used for languages that have computer generated speech. Gaidhlig uses actual recorded speaking people so the app cannot parse it into separate words to slow it down