
I'd skip walks for a week or two to begin with. Reduce the stress as much as possible, stress spikes and then hangs around and with him being super stressed everywhere you'll need to remove as many triggers as you can - so if he's spooking at you indoors and at people outdoors, then you can remove the people outdoors (so to speak), that will take a good chunk of it away. With time he should settle a bit but help him through it as best you can - keep curtains shut so he can't see people going past, every time you leave the room make it a really good experience (chuck treats, leave a kong or his favourite toy (keep it out of sight to make it more special) for example). Manage things as best you can to minimise spooking.
You could turn that into a training exercise too - stay in the room, by the door, and reward for any calm/happy behaviour or body language there; then step halfway out, and reward the same; then all the way out them immediately back in, and reward good stuff again; and so on, practicing with you popping in and out, gradually increasing the time so he gets used to it again and it becomes fun. Basically treat it as separation anxiety, which it sounds like. Distract him when he starts spinning too - play a game, do some training, or just sit and talk to him and feed him. When my collie is freaking at a noise I either send her for a ball and we play up the stairs, or I just stroke her and talk her through it - for a big spook I always do that, as she's too wound up to process the idea of going to find a ball.
It may be worth giving him something to help his nerves in the short term - many options for that, valerian tincture, skullcap & valerian tablets, rescue remedy, serene-ums for example. Or any of the multitude of stress easing herbal mixtures on the market - it's all down to what suits the individual dog. You may not need anything as it is not long since the incident happened, but with him being as stressed as he is I'd certainly consider it. My personal favourites are valerian tincture and melatonin, but the latter is harder to get hold of.