They are also sensitive to transport shock, so if you buy a big group of them at one time, get the LFS to split them up with no more than about 4 in a bag. I have 6 Rummies in my 55g but I've bought probably 10 others at various times that didn't make it. My 6 are troopers. Keep the bag out of alot of light to reduce the stress and they should be fine. That was recommended to me after I lost some in the past.
I think they will adapt to any pH as long as its stable. But they may prefer a pH in the range stated above.
In a 29g, I'd go with a school of 8 if you have the room. They are a great, tight schooler.
Awesome fish! They can be sensitive but otherwise once they're acclimated they're not hard to care for. I like odd numbers for schools so I would go with 7.
When they're happy, their heads will be totally red. When they're stressed, the red can be completely missing.