Put xexmenu on a xbox formatted usb stick using Horizon on your PC.
Put the USB stick in your Xbox.
Go to System Settings, then to storage, select your xbox formatted usb stick.
Go to Demos
Find xex menu, and move it or copy it to your internal xbox hdd.
put dash launch, freestyle dash, and whatever other homebrews you want to have on a fat32 formatted usb stick.
put that stick in your xbox.
navigate to xex menu under games, open it up, use it to move the aforementioned homebrews to your xbox hdd, then uses xex menu to launch dash launch, and use that application to set everything up, most importantly, setting freestyle dash as your default, so it boots into that automatically.
You, personally, will most likely never need your original NAND image.