Phrases- Please help.

Hi,

1) Beginning a sentence with the word FOR. For the majority of the time I have known Matt, I have been friends with him.

What type of phrase is this? If it isn't, what is it?
Is it alright to begin with the word FOR?
Is the comma essential?

2)Being- Is this a gerund?

If so, it should be 'my being here', and not, 'me being here,'correct?

3) It is a battle we may never win highlighting what a great guy Matt really is.

This is a participle phrase, correct? A particple modifies a noun or pronoun- in this case the phrase is describing Matt, but he is not mentioned in the main clause, so what is it modifying? So is it still a participle?

4) We have actually become great friends sharing passions which include poker, clothes, music, drinking

Because the word sharing is the ing form, it is a verbal/non-finite verb, correct?
What type of phrase is this then?

Thanks a lot.