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You had to wait for the updated file, too ;) Are you skipping firmware update by default?
Now the CatalogURL is there. It was there when I wrote the script. And yes. Firmware upgrades are skipped.

Note: Folks. The preferred way of installing/upgrading High Sierra it to use the App Store !!!
 
Is it only via App Store, or can I download it via Apple Developer site? I couldn't find DP5 anywhere, and I need to install it on 3 Macs and can't be bothered downloading it three times...
 
Was you storage SSD or HDD ? and did you set anything or does it give you any kind of option ?
SSD 2017 MBP, no options just upgraded, chose HD and installed.

Edit: No issues using APFS for me BTW.
 
Is it only via App Store, or can I download it via Apple Developer site? I couldn't find DP5 anywhere, and I need to install it on 3 Macs and can't be bothered downloading it three times...
Once you have downloaded you can use createinstallmedia from the command line to create a USB installer, or you can copy the app installer to the computers you wish to upgrade.
 
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