Hey
look to posts below I asked for a seven button layout for a similar situation as you recycled past gave me a template for a 6 button lay out and I found that it had to be adjust as the buttons were too far apart.
The original template he gave me the buttons were 1.75 apart (center to center) and I had to redo it, so I went with 1.5" (center to center) apart and I am still not too sure this is going to be comfortable enough.
My suggestion is to just measure it out on paper and use the template on top of a shoe box.
Just my 2 cents.
Ed