Yeah 6 will be fine, and since you're adding plants and rearranging, it won't be "their" territory anymore as Sena said, they'll be establishing new territories- they do this any time they are re introduced after being separated, had their tank rearranged, or have new fish added.
Remember to clean the tank well, go for density, feed them a lot for a meal or two before you let them out, and I bet things will be good. He's a photo of my tank for reference as well :)
A word of advice when picking up plants: often times plants sold at chain stores are not aquatic at all but are labeled as such. For live plants some good things to look for are hornwort, camboba, amazon swords, java moss, duckweed..just to name a few.
Good luck, feel free to PM me with any questions or comments and keep us updated!