How to install guix system from existing linux with guix package manager?

[kiasoc5]

How would I install Guix system from an existing Linux that has the guix 
package manager on it (aka from a foreign distro)?

Specifically I have Guix installed on Arch Linux on an encrypted btrfs ssd. I 
have a @home subvolume mounted on /home. Currently /gnu/store is not a 
subvolume, but I'd like to reuse it for guix system. I also have the efi system 
partition for uefi boot.

What I'd like to do is install Guix system and boot from a subvolume. Ideally 
the guix fstab would be like this:

@guix-root is mounted on / on guix system
@gnu-store is mounted on /gnu/store on guix system and shared between arch and 
guix
@home is mounted on /home and shared between arch and guix

So I think the steps are as follows:
0. backup data (just in case)
1. move /gnu/store to subvolume
2. install Guix system manually with the following file systems:

(mapped-devices
  (list (mapped-device
    (source (uuid "my-uuid"))
    (target "cryptroot")
    (type luks-device-mapping))))

(file-systems (append
               (list (file-system
                      (device (file-system-label "cryptroot"))
                      (mount-point "/")
                      (type "btrfs")
                      (options "subvol=@guix-root")
                      (dependencies mapped-devices))
                     (file-system
                      (device (file-system-label "cryptroot"))
                      (mount-point "/gnu/store")
                      (type "btrfs")
                      (options "subvol=@gnu-store")
                      (dependencies mapped-devices))
                     (file-system
                      (device (file-system-label "efi"))
                      (mount-point "/boot/efi")
                      (type "vfat")))
               %base-file-systems))

3. configure uefi to boot guix grub by default

WDYT? any tips/suggestions?