Glad you could vent with us :) We all need that once in a while. Sounds like you are doing a lot of things really well. The thing that jumped out at me was it sounds like there are a lot of things that could be better childproofed. There are wonderful toilet lid locks (One Step Ahead), the shower curtain should be hung up out of reach, all the kitchen cabinets and drawers should have locks except for one where you can keep plastic tubs or pots that you don't mind him playing with. Blind cords should be fastened to a tie off point high up or use the cord keepers from One Step Ahead. Eliminate as many "no-no's" from the day as you can so that you can help him focus on a few basic safety rules (like not running away in traffic situations) rather than constantly having to discipline him. Shower at night when he is asleep, put toilet paper up out of reach.
Some kids need more childproofing than others. I remember my SIL being so surprised when she had to childproof for her 3rd kid, the first 2 never touched anything they shouldn't but the 3rd was quite spirited. Limit the time-outs to a few critical rules, they don't make a lot of sense to most 18 month olds. If he isn't verbal much yet, teach sign language especially regarding things like meal time so he can ask for milk instead of screaming. Give lots of hugs even when it seems crazy, it will make you both feel better.
Continue to get him outside as much as possible, put on your running shoes and find a huge field. If you have any parks with ice rink walls still up, they work great because there is only one opening. Focus on getting more sleep for you.
Only keep out a couple bins of toys, put all the rest somewhere safe and rotate every week. Let him dump them as it is developmentally important at this age but then get his help putting them back in so he can dump the same bin again.
Hugs, good luck, and hang in there.
Signed, mom of a spirited child with sensory processing disorder :)