I’m going to be a freshman in college in the fall and I can’t decide if I should introduce myself on the FB group. A lot of students have already. Have you actually made friends using the FB group?
I have! I’ve actually made a good number of friends on my college’s FB page and found one of my suite-mates, too. I was hesitant about doing the whole intro paragraph post thing so I actually didn’t ever do that - I commented on a good number of posts, like if anyone was in the Honors College, in my majors, or in my hall and I got to know a bunch of people with similar interests. I also joined a lot of the GroupMe groups that were created and met a lot of people like that too. Eventually I did make posts on the group - is anyone else in this orientation session? Is anyone else in this hall? and I got to meet a lot of people! I wouldn’t worry about introducing yourself, just jump in.
Doesn’t hurt to introduce yourself.
Be aware of what you say and how you present yourself. You want to make a good name for yourself.
I already did. Although, I seldom post in the group page out of fear of becoming too known. 
Yes, but be smart about it. I’ve seen this one guy known and distanced by his ENTIRE graduating class (and several members of other classes, because we were told about him) because he would not stop posting videos of himself awkwardly and horribly freestyle rapping/singing
I don’t post in the group that much, but quite a lot of people have messaged me, and I have actually met a couple of great people! I think it’s good that you won’t be meeting complete strangers once you arrive on campus.