For a start, no viruses that will affect your Mac system or programs. However that does not stop you transferring viruses.

If you are a strong iTunes user, I would still recommend some backup players. You are probably aware iTunes cannot play certain types of files. These include mp3pro, ogg vorbis, wma, real, flac, ape, & some others. So I'd recommend a backup player. Vox though small & simple will do a decent job at playing such files. Check this list: Alternate Audio Players & support plug-ins. Vox can also convert audio files into other formats.

It is possible to get a 3rd party plug-in for iTunes that allows you to import & play Ogg Vorbis files in iTunes, however such files would not be compatible with iPod.

For audio file id3 tagging, iTunes has limited abilities. I usually use Media Rage but it's not free. It will work in conjunction with iTunes by auto-updating its library.

For Video, I'd recommend VLC & Perian; http://www.gnutellaforums.com/292880-post4.html Though I also use MPlayer as a backup player. (I use Flip4Mac pro version also.)

Are you going to be using LW 5 or 4? LW 5 for OSX does not handle large quantities of shares very well at present. LW 4 seemed to handle 4-5 times as many shares much better. Not to mention LW 4 has more tools than the present version LW 5.