SoFloFlame, if you still have a whitefly problem, they're attacted to the color yellow, and you can find some yellow sticky cards (at hardware stores) that will take care of them. I've used them indoors with pretty good results.
Yeah, 18" is a good target...unless you completely stop feeding them nitrogen, they'll continue to grow...I've mistakenly continued to give my plants N well into the flowering stage and those plants almost outgrew their closet...had to keep lowering their shelf LOL...
Good luck!