how many fraternities to express interest in

I wouldn't sweat it. I would check all that you are interested in, whatever it is.

As for old row, they aren't what they used to be and there are better new row houses out there. Seeing you are not from the South, give it a shot but I wouldn't hold your breath. No loss though.

Honestly I think you’ll have more fun in a NR house. There are a lot of GREAT NR houses that aren’t just a bunch of mountain brook guys who’ve known each other their whole lives. If you’re in a decent/ good NR houses you will have just as good of a social experience (if not better)

Look at New Row houses. You'll have a better time. Popular houses known to have northerners are Pike, maybe EX, Beta, DX, KE, maybe Pi Kapp, LXA.
Though these houses have northerners, they still have a lot of Southern tradition to them and have long histories on campus.