One Computer, Two Accounts - How Best to Proceed with MacOS 10.8.2?

Question

My wife and I want to share our new iMac, and I'd like some advice on how best to do this without messing things up.
We both have iOS devices to sync, and we both are using the same iTunes Store Account. However, we each have our own iCloud account. We each have our own email accounts, Hotmail accounts, and Yahoo accounts. We each have our own account for the iMac, which I assume you would need if you wanted to maintain two different sets of Mail accounts and two different Facetime "accounts," what to speak of different desktop customization options. 
Things we would like to share without duplicating files include: iPhoto library (~100 GB), iTunes media files (over 300 GB), Contacts list, (maybe) Calendar, and (maybe) Safari bookmarks. We do NOT want to share e-mail, Reminders, Facetime. Ideally, I would like for her to be able to sync her devices entirely through her iMac account. However, I am not opposed to her syncing her iOS devices through my account for some things and through her account for other things, if that is not easily avoidable.
Regarding the iTunes library, I could go either way on her having separate library files with separate ratings & playlists or just sharing the same library setup that I have. However, I would want her to have access to the same metadata that I have for all music and video files, since I have lots of custom album art as well as lyrics loaded in. Do we have to use the same library file in order to have access to the same metadata, which will be updated on a regular basis?  If so, then is there a way to do that via two different computer accounts, or does she pretty much have to sync with my account?
Now regarding iPhoto libraries, I wouldn't mind us sharing the same "library" as well as the files, including ratings and albums. I would like for the "faces" setup to be the same for both of us, if possible, so that she does not have to repeat the process of face tagging. I read in an older article that sharing the iPhoto library could be accomplished by sending the iPhoto library file to an external hard drive, but as that seemed to be an older approach, I thought I would ask here if that is still the ideal approach. I might want to send the iPhoto library file to an external HD anyway for space considerations. But if I do this, and we are both using the same library file for viewing photos, then does she still see the same albums, events, and tags that I have created already?
Is there a way to share contacts and calendars without having to share other things like Notes and Reminders? I suppose I could have her sync this information via my account, but I'd be greatful to learn of a better way if there is one.

Answer 1

You can share out both the iTunes library and the iPhoto Library in their respective preferences. However, the sharing account must have both iTunes and iPhoto running. You can keep the account running with those things open in the background using Fast User Switching. Enable that in the Users & Groups system prefs and then never log out, just switch to the login screen or the other account using the Fast User switching menu.
I haven't done much actual use in either, so I don't know what the limits are (like making a playlist out of the shared tracks, syncing with iPhone/iPod, etc). For iPhoto, all the photos are available, but if you want to edit one, you have to import a copy into your own library. Another option might be to not keep the media inside the Library, but store it in the /Users/Shared folder. Then, set up your Libraries to leave the content where it is (Preferences). However, I don't think you'd get the metadata for the iTunes music. I believe that is all stored within the iTunes Library.
You can share iCloud calendars so the other person can see your calendar by right-clicking on the Calendar name. There will be an option to share the calendar, there. Also, you can do so from the iCloud web interface.
I've got nothing on sharing contacts. Not sure of a good way to do that besides maintaining two sets. You can start from the same source, but it will diverge over time as contacts are added and removed individually.