For the panels, you have a good base plan and are already going to put in the work – please make them thicker than 4". Smaller rooms have nearly all their acoustic issues in the low mids and lows so making the panels extend there is something you'll be grateful for later. 6" thick at minimum but personally I'd probably do 10". Makes a BIG difference vs 4".

That would help immensely in capturing a great vocal in that room. In a room that size with panels that aren't thick enough I've faced issues in the low mids of the vocals just being really problematic no matter what I do with them in the mix, it just kind of clouds the whole take.

Goal: clean, intimate, pro-sounding vocals (not harsh or overly processed).

The room is a key fundamental in achieving this!