+1 for LittleBettaFish's post.
Tall plants are best because they help break up the line of sight, preventing too much chasing. I have 7 girls in my 55 gallon community tank, and one side of the tank is densely planted with one enormously tall amazon sword (over 2 feet tall), and a dwarf lily plant with lots of lily pads. The other side of the tank has some tall red ludwigia, but also some short swords (two of which will get taller), an anubias plant, which I believe gets longer but not taller, and some Wisteria, which is short now but will get tall.
Plants are not difficult when you have the right lighting. You can even get some tall silk plants as well as moss balls and betta bulbs. Some of the fake plants can look almost real.
In my sorority I have one female I had for about 8 months, another female who I've had for about 4 months, 4 that I bought from Petsmart in one day, and then I even added one 3 days later because I saw it in the store and I couldn't resist. She's like, pinky-orange with blue iridescent rays in her fins. Anyway, they all get along very well so far. It's been about 3 weeks. I didn't even have much of a problem when I added the new one 3 days later. She asserted herself but wasn't violent or anything, and she didn't get picked on, either.
I'm not sure about the odd-numbers thing.