Firstly, the download is hanging because the installer still has the old URL definition for the download site which was changed a while ago. A bug has been raised on this and the URL in the installer has been patched in the next branch of the repo which will be in CU175.
Secondly, normally the installer should install everything from the iso that you downloaded. If the installer is trying to download it from the IPFire download site this is an indication that the iso is likely corrupted. It shouldn’t happen with any CU iso file.
When you downloaded the iso did you confirm its sha256 hash that is provided on the download site. This is always worth doing to ensure that the download went without a hitch. I have not had it often but it has happened that the sha256 hash of the downloaded file was different and on re-downloading it was then correct.
I am presuming that you have the iso on a usb stick. How did you copy it on to the stick. I have never gad a problem with dd but some people have reported problems with Balena Etcher or Rufus. Maybe redo the copy to the usb stick.
Attempting to download from the url is a sure sign that there is a problem with accessing the code in the iso.