I've never heard get-go, I'm going to guess it is street argot ;-)

Yes - it has the same meaning as beginning, but is a colloquial alternative.

"from the get-go" is "from the beginning" in a temporal sense. I cannot think of a situation in which one would use the phrase to mean beginning in a physical sense. "From the get-go" I believe is an adverbial phrase that you can use in either the first position in an English sentence, or you can use it after the verb (direct object). It is used primarily in American English, but many native English speakers from countries other than the US will recognize it due to mass media, etc. If you use it in the first position, it sounds more literary (although paradoxically not more formal), and is a construction that comes from the English language's German roots. Another variant of the phrase is: "from the very get-go." The correct phrase would be: "to have trust in someone from the (very) get-go", or "to trust someone from the (very) get-go." Any of these variation would work in English: I trusted him from the (very) get-go. I had trust in him from the (very) get-go. From the (very) get-go I had trust in him. I had faith in him from the (very) get-go. From the (very) get-go I had faith in faith in him.

I've heard 'get-go', but I've never used it. It's more common in informal American English than in other variants. Remember that a standard phrase such as 'From the beginning' will always be correct and appropriate - a colloquial one will not. You can always replace an informal or slang phrase with a standard one, but the reverse is rarely true. For example, you can say 'I read this book from the beginning', but you couldn't use 'get-go' in that sentence. You could use '...from the get-go' in the phrase you suggest, but please don't think that it's a synonym of 'beginning' in all cases and in all contexts.

I trusted you from the get-go