From what i gather/gathered

Lastly, is from what i've gathered correct too and what is the difference from the others?

No, it is not wrong. In the present, it means from what I have come to understand. In the past, the information is what I had come to understand.

From what I gather, the weather will be tonight.
From what I gathered (in some previous conversation probably), he was still mad. Or from what I gathered, he is still mad.

It all depends on if you want present tense or past tense:

gather = collect

I save the best grapes from what I gather in the vineyard.
Last year, I saved the best grapes from what I gathered in the vineyard.

gather = learn from observation or study

From what I gather, he seems like a good person for this assignment.
From what I (have) gathered, there we

Hi. I have a question.

You just happen to be hanging out here?
You just happened to be hanging out here?

She just happens to be hanging out here.
She happened to be hanging out here.

Which is right? Thanks

Hi. Anon:

You just happen to be hanging out here?

You just happened to be hanging out here?
Neither one of the above has the proper form for a question.

She just happens to be hanging out here.
She happened to be hanging out here.
The above are OK.

From what I gathered is right.

So is From what I gather.

Please read this thread carefully.