How to make a restore image / export ISO to restore later?
Answering the last paragraph of your question first

Since you have rooted the device, flash a custom recovery meant for your device  (Google on XDA for your specific make and model) and take a nandroid backup (click on that tag and read the wiki) and restore /system to restore the way it is

Next, factory-reset will not undo the changes you made to the /system, it only affects /data. Which means apps you uninstalled will not be installed but yes your launcher settings will not survive. That's why it's better to go for Nandroid backup to restore with minimum effort

Edit Your device has official TWRP. Make sure you read the dm-verity warning