One of mine had tantrums like this when 7/8 and it was terrible, a lot worse than a toddler which at least you can pick up and move if they are kicking off.
I did come down very firmly though, on throwing/kicking/hitting- one day off the computer for every single time that occurred. I only had to do this one long time - I think we clocked up about 15 days before she finally calmed down. It was a long two weeks but sent the message- you never ever hurt people in our house.
The other thing that worked was getting my dd to stay in her room- I told her she could be cross and angry up there, say bad things, but not hurt me or anyone else (or things) and she had to stay in there til she calmed down.
This gave her a bolt-hole. I would suggest your dh back off and leave your son to it so he can calm down, but I don't think you should feel bad about how you both handled it this time around it probably took you by surprise.
YANBU to have a tired exhausted 7 year old have a tantrum, you are a little unreasonable if you don't lay out the consequences of what will happen if he hurts things or people during any other tantrum, otherwise, what's to stop him doing this when bigger and stronger? I would let him know this now and plan how you will handle it if it happens again.
It is mighty stressful, I used to feel like I had been in a boxing match when my 7/8 year old kicked off and like no-one else's children would be still doing this at this age. She's now a delightful 10 year old, who may roll her eyes a little, but wouldn't have this type of tantrum, so it is not set in stone.