That smells like a mirror problem. I can’t do anything about it, just tell you that we have improved the mirror choosing in the upcoming Cnchi 0.10 release.
For what is worth, in my tests Cnchi never gets more than 30 minutes to install Antergos (I’m in Europe, if that counts).
I decided that first the "Can’t install necessary packages. Cnchi can’t continue. " error should be fixed before mentioning another problems.
What is there to fix? This error means that Cnchi can’t download or install the packages needed. Then, in the log you can see which package couldn’t download/install. Again, there’s little we can do about this, because most of the time is a mirror problem (mirror is not updated or not working at all). Cnchi tries other mirrors in this cases, but if the non updated thingy is the package database, there’s nothing to solve this.
Again, new Cnchi 0.10 has new downloading code, that will tell the user the downloading speed, but there’s nothing we can do about non updated or faulty mirrors.