Also bootmii as an IOS won't do anything for you in terms of brick protection. If you can't install it to boot2 on your system, you can't get brick protection from bootmii.
Making a NAND backup with the IOS version will basically just give you a LAST resort before sending your wii to nintendo due to a brick because you will be able to use a hardware NAND programmer to flash that backup directly back to your chip.
So if your Wii can't install it to boot2, your only option for brick protection is preloader, which should not be installed until after you update your system and do any patching to IOS60 because updating will remove it anyways and patching IOS60 will require you to reinstall it anyways.
If you are afraid of bricking read through everything in my guide and then continue. Knowledge is the best protection against bricking and preloader is there for any of the other possible bricks (besides like power failure during updating or something beyond your control).