I am a recent emigre to Mac.. and came in just at the point of swap over from Snow Leopard to Lion.. I am happy I stuck to Snow Leopard. So I do not have the info you need. I know all about the inside of the TC because I repair them.. a couple of hundred anyway. and even some Mac computers.
iTunes should be no problem.. according to the continual annoyance of upgrade to OS.. itunes.
What's New in iTunes 10.6.3
iTunes 10.6.3 includes support for OS X Mountain Lion and addresses a number of important issues:
• Addresses a problem where iTunes may become unresponsive when syncing an iPad (1st generation) that contains an iBooks textbook
• Fixes a problem where photos synced to a device may appear in an unexpected order
• Resolves an issue where iTunes may unexpectedly delete playlists created on a device
• Fixes issues where iTunes may unexpectedly delete apps on a device
• Improves overall performance and reliability
So it should run on Snow Leopard and work identically.. YMMV ..
iphoto is version 11 in both.
In SL machine it is 9.1
In latest version for Lion and ML it is 9.4.3.. I would not know if the libraries can be interchanged but I would say it should.
Look at the documentation for setting up network sharing of the iphoto library as that may make it clearer.. but you should ask for specific help in iphoto area.
http://support.apple.com/kb/PH2435
http://support.apple.com/kb/HT1198
https://itunes.apple.com/au/app/iphoto/id408981381?mt=12
You can do an install of the SL to an external drive and simply change target boot drives.. that allows you to change back to SL on a trial basis to see if it works.. rather than blow the machine away and discover later what you want is impossible to achieve.. after a long time in computer support.. I find it much easier to simply do new installations on new hard drives. Then any changes I make to a PC and any old files are totally unchanged.. Hard disks are cheap. Buy FW800 for your old iMac as it is still fast and will give you a good idea.. if you like it you can transfer it to the onboard drive..