I'm not sure if this is possible anymore, but for a while, there was a way to copy over the compiled base system from the disk instead of compiling it all from

I'm not sure if this is possible anymore, but for a while, there was a way to copy over the compiled base system from the disk instead of compiling it all from scratch. Running your first emerge -vaDu world might end up recompiling everything anyway, depending on the age of the ISO, but you didn't have to do any compiling to get a base system deployed.