Re the flush or recessed front, in my personal experience, there's no substantive difference. The recessed front isn't recessed enough to act as a flag or barn door, it's just a design thing with no real purpose.
Again from my own experience I prefer white as oppesed to silver. The silver reflects a minor bit more light, but can be a more on the spectral side and avoiding spectral light is why I'm using the softbox to begin with. A gold insert can be useful.
Quick set up is important if you go on location a lot, but mine are pretty permanently set up, so that isn't a factor. There is one I would recommend if I could recall the brand name, but sadly I'm old and have too few gray cells left. It was the size you are considering, but had the capability of mounting barn door type flaps to either side. Unfortunately it was stolen from my car a good ten years ago. I have not seen one since then, but I know they exist. Being able to mount a large barn door, almost like a gobo on the soft box itself is a real plus in light control.