First up, if you intend on reinstalling all the same applications, configs, etc. then why do a reinstall, you won’t gain anything outside of porting your setup to a new install (if that’s all you want then ignore this and read on).
It’s not incredibly hard to clean an existing installation if you’re ok to fix some minor breakages, the other approach (reinstalling) is the more standard means of doing this though.
Firstly I’d recommend using a dotfile manager which can make backing up and restoring files easier (shameless self plug dfm) or do it manually with [insert preffered method of file copying here].
Once you’ve got a backup of the things you intend to port to new installs then setting up said install is a matter of reversing the process or using the relevant flags of the dotfile manager to restore them from the new install.
Crucial - When creating configs that you intend to be used by multiple users you have to take care to not hard code anything.
To get all the same applications some people create a dumpfile for both official and AUR packages and store them with their dotfiles, I’ll show how to do this
# create dumps of current explicitly installed packages *(not deps)*
pacman -Qqne > official_pkgs
pacman -Qqme > aur_pkgs
# later to re-install said packages using the dumps
pacman -S $(< official_pkgs) --needed
[insert AUR helper here] [install flags] $(< aur_pkgs)
# eg. on a stock ArchLabs install we have baph, so you'd do
baph -inN $(< aur_pkgs)
Lemme know if you run into issues or something wasn’t clear,