It sounds like you're having a rough time. The 4 month sleep regression is hard as their sleep patterns change forever.
i would still demand feed but would introduce some solids and a pre-nap and pre-sleep routine so he knows he's meant to sleep at the end of it.
I would personally start by not rocking or feeding to sleep, but putting him down at consistent times each day, after a consistent routine and sit with him and pat (or rub) his tummy, making a shhhhhh noise (or white noise). That way he is falling sleep where he will wake up and is more likely to resettle (though this may take some time.