i would suggest to do the following. On your current system i would create a new subvolume called "root_antergos"or something like that. During the Antergos install you can then mount this subvolume with the mount option subvol=root_antergos. This way your old “/” subvolume will be untouched and you won’t run into trouble with your old linux-root data. After installation you should then include the “subvol=root_antergos” in your new /etc/fstab. And when your new system is running perfectly you can then delete the data from your old “/” subvolume.
I usually don’t install any system in subvolid=0 because i “learned” it that way under ubuntu. I like the ubuntu idea to create all subvolumes (ink root) inside the subvolume with subvolid=0 and mount them where they need to be (/ /home /usr/local/ /var/) with lines inside of /etc/fstab.
If you need more help just just let me know!