Cannot download anything in Mojave from factory
Apple offers 90 days of complimentary support and setup assistance so you qualify for free online / phone support to make amends. You've clearly got something that's not even close to happy, so this isn't the on boarding experience that was designed (clearly)

If it were me, I would just boot to recovery and erase and start the setup over. That takes about 15 minutes plus however long it takes to re-download the installer. It's often much harder to determine what went wrong and if you have a new machine, a fresh start will let you know right away if it was just some things that didn't get set up, a poor image of the OS or a very rare case of something not right. Getting Apple involved sooner if you're not sure how to erase would be my winning move if I wasn't super comfortable with recovery mode.


https://support.apple.com/en-us/HT204904
Reinstall Mac OS X Mountain Lion before selling a Mac
Trying to reinstall OS Sierra
Can I install an older OS X over a newer OS X without restoring from backup?