Definitely get your puppy from SPCA or Hong Kong dog rescue. Yes most dogs are mixed breed but I adopted my husky from SPCA so you just need to keep an eye out there.
Firstly research the dog breed to make sure it fits you. Husky's for example are more independent and they could really care less about coming up to me and saying hi. Whereas my mixed breed is always excited to see me. Certain breeds bark more, need more exercise, need more attention, etc.
Cats can be left alone but dogs need to go outside unless you plan to come home to pee and poo in the house everyday. Not too fun.
You can train your puppy with positive reinforcement about pee and poo outside. I did it with my two dogs and they learned quickly. I gave treats when they went outside. You take them out after they eat/drink and in the morning is the best. Control the hours which food and drink are available then you can have better control training them. Having water out all the time is good but in the beginning we limit it because they drink all day then need to go pee every 5 minutes.
Ive known some locals who think dogs can just pee and poo in the house on those pee pads. It's true but really it is smelly and dirty so do know that once you train this way it will be difficult to change it. This might work with small dogs but definitely not with larger ones.
During the first two years. Dogs eat a lot of stuff. Your furniture, your sofa, even my dog ate the electrical wire and still has a spark on his nose! So just be aware that anything you leave on the ground is fair game, shoes too! So don't be too upset. Make sure they have their own toys but they will still eat your stuff. This behavior slows down about 2 years but sometimes things can not be resisted even later on.
How to introduce to your cats. I would get a crate. Crates can help for training too and prevent them eating everything but try not to leave them in the crate too long.
So puppy stays in while you are out and cats get used to him. Then you have supervised play time. Probably don't try to take them all outside together. As time goes on you use the crate less and less. Now my crate is open all the time but the dogs like to go in there now and then. My husky is pretty much glued to it.
Good luck!