Tux or suit?

Suits are fine. I do think there is hype among a tux in the same way there is about having labels on clothes. It serves the same form and function. Most people might not even notice the difference. I do personally like the details on a tux, but you can get some really great suits. If that makes him feel comfortable, happy, and his best then I say go for it.

Some grooms don't wear even a suit.

I see nothing wrong with it whatever you guys are comfortable with. Ive seen many grooms wear suits and still stand out and look really nice.

We are going with a tux...

Wearing a suit is fine! My FH is wearing one. All the weddings we have been to had the groom in a suit and it wasn't an issue! If you're wanting him to stand out, you could always have him in a different color suit that compliments your wedding colors, or have him in a different color tie!

Guests should be dressed in the same formality as the groom, or one step down. If he wears a suit, no one wears a tux. Get him a very nice suit. Consider a less common color if you want him and GM to stick out. Midnight blue rather than navy, or burgundy. In summer, white or very light tan. And go for something more elegant in fit, not the supersnug Pee-wee Herman fit that is trendy but not classy. Something elegant with some drape, not everyday, and he will stand out . Consider a hat if he wears them.