I need advice on my cat

About a month ago I got a cat from the humane society. His name is mylo and supposedly he is 5. I highly doubt this just because he is quite hostile and lovely to bite everything he sees. They found him near a barn and I think he was definitely outside for a while. He hunts nearly everything he sees. I’m not sure how to make him less hostile. Especially because I love to bring people by my house but I have to warn them now if they want to play with my cat. He’s not always hostile, sometimes he likes to cuddle but inevitably he will go for your hands or legs for some reason. Another thing about mylo is since I got him he farts constantly. And these farts are extremely foul. His shits too are watery and he seems to be in some sort of discomfort. When I got him from the humane society he already was pretty poopy but I thought once I changed his food over to this nice expensive food he’d be good. The food has quail, pomegranate, and pumpkin in it which I know is very good for cats with upset stomachs. I know I should bring him into a vet but I’m about to lose my job and thought I’d try and get some advice first on maybe something I can do in the mean time. Let me know if you know of any behavioral help I can do. I hate disciplining him and he usually takes it as play. Or if there is some sort of food that has help your cat in the past would be greatly appreciated