CoNgRaTs on getting a new puppy! How exciting!
I think the set up you describe will be perfect. Are you going to be able to let him out often during the day or is he going to have to stay in the xpen for a large number of hours? If you can let him outside to potty every 2-3 hours, I wouldn't bother even using wee wee pads. On the other hand, if you won't be able to let him out that often, then putting a wee wee pad in the xpen is probably a good idea. The only thing I worry about it being in a litter box is your new puppy may not want to jump in that box. He looks so tiny and the box may intimidate him. I work during the day, so I have a large crate that I put my puppy in. It is basically the same concept as an xpen bc it is large. But I fold a wee wee pad in half and put it in half the crate and then on the other half I have a bed. That way, there is no other place she can go to the bathroom but on the wee wee pad. Then when I'm at home, I make her go potty outside. Eventually I'll take the wee wee pad away altogether. I just don't want to her to potty all in her crate when I'm gone.
I would wait a week to bathe him. You need to let him get adjusted to his new home bf you do something traumatic to him like his first bath. Then bathe him once a week unless he has really dry coat and skin, then I would only do it ever 10-14 days. Make sure you use conditioner! It doesn't really matter what kind.
I don't brush my dogs' teeth, so sorry I can't help you there!
At least the first couple of weeks, I would give him NutriCal every 2-3 hours. These dogs are VERY susceptible to hypoglocemia, so you need to pay close attention to him to make sure that he is eating regularly and eating well. Then supplement his diet with NutriCal. If he won't eat it on his on off your finger, you will need to rub it on his gums or on the roof of his mouth. If you give him NutriCal regularly, he will not have a hypoglocemic attach.
If you have anymore questions, just let me know!

I know it is such an exciting time and I'm sure you'll have lots of questions! You can do a search for anything here on YT and I am sure it's been discussed. You can find out TONS of info just by doing a search.
GOOD LUCK!