At first the three ones are all inverted sentences.
The original forms are “We are go!
We are here!
and You are here.”
The means of the original forms seem to be ease to understand ,right?
Then
“Here we go!”means“Let's begin( to do sth.)"。
“Here we are!”means, ok for example,
“Here we are at the station!”「さあ、駅に到着したぞ。」
But“So here we are again.”「さあ、また始まったぞ。」
So it's better to make out the meaning of“here we are " case by case.
And“Here you are!”means「どうぞ」or「It is for you.」
“Here you are!”is simple to be used.People change “you ”to “we",maybe it listens more kindly for the guests. ~~c