Overstimulation causing reactive behaviours

I recently took in a rescue dog and as much as I understand that there is a decompression component, I'm feeling a little over my head right now. The rescue did not provide me accurate information, saying he was a 'happy boy' but I've gotten him home and he's reactive to EVERYTHING and becomes overstimulated super easily (outside, inside, with sounds or with toys) my biggest concern on this is that he has already turned the aggression on me a couple times and I am not okay with him attacking/biting me. I have noticed that the crate is super helpful for him to decompress and calm down but sometimes I take him out after an hour of him being calm and quiet and he goes straight back to overstimulation and aggressive behaviours. Obviously I don't think leaving him in the crate 70% of the time is a great way to live, I have seen some improvement since he's come home but there's still so much work to be done and realistically my biggest concern is the aggression towards me when there is no reason for it. Anyone dealt with something similar? I would love to hear some success stories.