Five 1-2in red heads in a 10gal will be fine for qt. Just be careful with overfeeding & stay on top of WCs. In regards to it not being a cycled tank, use some of the media from your cycled 75.
I've kept red heads in 7.6-7.8 pH
I am going to take out the media from one of the AC 70's on my 75 and put it in the AC 30 while the Geo's are in the 10 gallon.