christa, his poo will get smaller when you take critical care away. it will. it's a feeding change and it will affect his droppings. you could get some lactulose from the vet (it's dead cheap and it's sweet so they like to take it) and give it to him during the transition period - it lubricates the insides so you avoid hard dry droppings.
long term syringe feeding will cause teeth overgrowth and root overgrowth - this will cause huge problems (not just dental) and it will be extremely expensive. when teeth are not worn down properly, they get sharp spikes that dug into their cheeks, cause tongue lacerations and can even trap tongue - this will all prevent him from wanting to eat and it's painful. if the roots overgrow into the top arcades, once they're in the ocular spaces or sinuses, the only thing you can do is put them to sleep.
i know you're scared he'll get sick again but if you continue syringe feeding, he will, even though you think you're doing the right thing. and i understand the vet bills too, you've been amazing paying for his hospitalisation and all the treatment he's had, a lot of people would not have done that. but if he develops teeth problems (and he will if he's not on solid food), it will mean more vet bills and dental bills are not cheap.
i would go with lactulose. it works extremely well and you don't feel like you're giving them medicine because they're so keen on having it! and it costs me less than £5. you can only get it from the vet though.