Dog training

I have a 3 (almost 4) month pit/mastiff mix who is VERY hyper and easily excited. My son will be born by the end of this month and I’m wondering tips for training? He knows how to sit and he’s currently learning Stay, he just get VERY excited and jumps and I still haven’t had a lot of luck in paper training :( he poops on the mat sometimes but never pees there and doesn’t give warning when he has to pee, only when he needs to poop. He also likes to take the couch cushions off daily to lay on the inside of the couch he’s weird

I’ve never had a puppy so I’m not quite sure what to do lmao, I’ve always adopted older dogs so this is completely new territory for me