I think it's best not To go overboard to start with . I bought loads of clothes that ended up a waste of money cause they out grew them before they were worn. I also bought beds and dog carriers that were too small in a few weeks . My advice would be get only the basics and add to it as you need to when puppy has been home a while. Main things are food, same type as breeder is feeding, you can change this later if you want but best let the wee one settle in first, a cosy bed and blanket with the smell of the litter on it, bowl for food and water and pee pads if you are going to use these. A couple of chew toys are a good idea someone suggested nylabone, if you are using these make sure it's the soft puppy one . The hard ones are really bad for their teeth causing breaking splintering Of the teeth. Wouldn't worry too much about lead and harness cause you can't take them out until after the immunisation anyway and if you wait you can take the pup with you to buy it making sure you get a good fit. Clothes are in my opinion not an essential nor are strollers, if you are taking him/her in the car, a good carrier is important , one that can be attached to the seatbelt to keep them safe. Just make sure to get one big enough to suit when they are fully grown. You will get lot of conflicting advice, just pick what you like and leave the rest
enjoy your puppy that's the main thing.