Thanks for taking the time to write some fantastic advice.
Two questions for you:
Did you lose anything from iPhoto?
Did you use Time Machine to upload your data after the clean install?
Thanks again for writing and for the feed back.
No i did not lose anything from iPhoto. Easiest way for you should be to do time machine copy or a 1:1 copy of your internal disk to another disk.
Check out carbon copy cloner if you are interested to do a "old school" 1:1
Making 1:1 backup is always a good thing even if you use time machine backup. With the carbon copy cloner backup, you then have a external backup which can be used also as a full bootable backup. Its never bad to have more than one backup
Anyways...
After you have installed your new clean system and made a new user account, you can use the
"migration wizard" program and it will see you have your old time machine backup (this point do not yet start using your old time machine disk as a new backup). From migration wizard you only select music,photos,videos..not any applications or other system settings. This should keep your new system otherwise clean but import your iphoto library(which contains your photos, events, faces etc). Same goes for your itunes library.
I would recommend you to do the time machine route, but remember. Do NOT RESTORE the time machine the normal way.
1) make sure you have current time machine copy of your system Even better if you also have another disk as carbon copy clone 1:1
2) Detach the time machine backup/carbon copy drive(s).
3) Boot your lion installation.
4) Erase the internal disk.
5) Install fresh clean Lion.
6) Create a new account.
7) Install system updates, tweak the basic system settings as you like.
8) Attach your time machine backup disk (when it asks do you want to use it as a time machine disk, answer NO at this current time.
9) Launch the "migration wizard" utility and choose to import from te time machine disk under your last user account.
10) Select music,photos and stuff you want.
This way, migration wizard will copy the old backed up iphoto,itunes library in right place and it will work just fine in your new account. This can also be done "by hand" if not used wizard. You just need to know what to copy and where.
11) After that check that you have all your stuff the way you like and manually copy other stuff if you need to.
12) When you are 100% sure you have all your important stuff off from the old time machine disk, you can use disk utility to erase the old time machine disk and then it asks if you want to start using it as a new time machine disk. You can then answer yes and it will start backing up your current new system.
UPDATE: Oh i seem i missed the point that you have itunes and movies on external.
It should be fine either way. You only then need to worry about the iphoto part when using migration wizard.
Because you have your itunes library already on the external, you only need to tell your new itunes to point to that external library.
You should have your external disk(s) backed up to another externals and disconnect them just to be safe