I guess I didn't really answer your questions...
1. Maybe a little bit, 35 to 50mm is not as bad of a gap, but either is workable.
2. No, there's no such thing as "too close" in varying focal lengths. Each lens has a purpose or useable range, and it's ok if they overlap.
3. Not really, but again I'd choose EF over EF-S lenses.
4. Yes, having a full frame lens is totally fine. With an EF lens you can add a film body for very cheap if you want to experiment. The extra coverage is not any detriment to a 1.6 crop body, and in fact the 1.6 crop uses the best part of the lens, so it's actually an advantage. In the case of the 60mm and 100mm, both are equally excellent optically, so it's more a question of focal length, working distance, how well it will hold its value, and whether it is useable on film or full frame digital.
5. Yes, you will find the extra "reach" of the 100mm lens a very handy thing when taking pictures of anything skittish.
6. Build quality on L lenses is better than on consumer grade lenses. Some are weather sealed, but the 30D body is not officially weather sealed, so it's not truly water proof. The body is capable of handling a little rain, as long as it doesn't get soaked. Yes, it's worth it to buy L lenses.