Looks good to me.
I don't bother with anything but normal mode, if it gets to that stage you'll be at the console, probably with an AIX install CD in your hand in case you need to do a maintenance or debug boot, and you can always use SMS to boot either disk.
There will obviously be some performance hit as the system copies the whole of hdisk0 to hdisk1 whilst also keeping up with any changes going on on the hdisk0 so try to do this when most people have got off of the system and outside of any busy period like batch processing or backups.
Talking of backups... take a couple of mksysbs before you start, ideally onto bootable media like an internal or at least native AIX tape drive, just in case it all goes wrong and you need to put it back together in a hurry.
Want tape help for the RS6000:
Couple of backups? - tape and tape drives are not the most reliable media so two is safer than one, it wouldn't hurt to clean the drive with a new cleaning tape and use new tapes for the backupe too.
All goes wrong? - even if you reboot frequently, and so fsck runs, it is not a complete guarantee that all of the data in rootvg is good and readable, so you may run into problems when doing the mirror if AIX / lvm reads a bad part of disk or a bad filesystem that has so far gone undetected because it is rearly read and never checked.
Be safe, be backed up - twice.