Not sure if this has been done before, or is common knowledge, or what lol... I searched for a while and wasn't able to find anything, so hopefully this helps someone else down the road who's in the same spot where I was a couple hours ago.
I needed a 3x3 button arrangement that could be flush from the wall, and could be raised one block from the floor.
Here's a view from the front:
And without the border.
You can extend the arrangement back as far as you want before splitting the signals off, with only one tile on either side, and two on top:
A view from the side. Redstone torches behind the top 2 rows, and repeaters behind the bottom.
Here's an example of how you might break the signals apart:
From the side:
Another view from the front:
This version uses no repeaters, but can't go straight back like the repeater version. It requires the side wires to come out one block each, making the whole arrangement two blocks wider:
Here's a link to the savefile.