New puppy advice/training tips?

I just had a puppy fall into my lap today. I want to keep him but I haven’t had a puppy in almost TEN years. My dog passed back in October and I really think she sent me this little guy to get me out of my funk because she got me out of a bad depressive episode when I got her almost ten years ago. Gimme all the training advice you have, I barely remember anything about training her because it was so long ago. Info on him: he seems to be possibly some kind of Pyrenees or Retriever mix, he’s going to be a big boy. Massive paws. Probably around 6 or 7 weeks. So far he’s slept a ton, peed once(outside and I gave him praise), I gave him some puppy food and he ate it. No poops yet. He does have some fleas, I washed him with dawn dish soap and will be calling the vet Monday to set up an appointment.
I also have 5 cats and a geriatric dachshund. Advice on introductions and socialization would be greatly appreciated, right now I’m keeping him separate from them. TIA!