I am not sure I ever had a definite Plan for stocking my tank, I knew I wanted a couple of Tangs which is why I converted my 300g to Salt and migrated the 75g into it. I knew I wanted color, lots of it because that is what attracted me to salt tanks in the first place. After that it was more of a Walk thru the LSF and see something I Liked, GOOGLE see if it was compatible to my tank and what I need to know to care for it, and if it works for my system, I'd buy it.
Now just recently, April 30 my birthday, I saw a beautiful Chocolate Mimic Tang. I'd told myself after my tang gang bullied the Regal I had and didn't let it eat so it starved last November I was done adding fish, but he is so pretty! So then I figured for sure I was giving him a death sentence, so I named him OJ, thought maybe Justice would Prevail, in my mind at least LOL. As it turns out, he is the 2nd biggest fish in my tank at 6 inches and my Vampire Tang is so laidback he moved out of his "sleeping spot". The Vamp acted pretty stressed for about 3 days and then he settled down, now they are all living peacefully together.
So, probably impulse motivated more than anything.