#1
I'm interested in LZ (contrary to my avatar) and what are the difficulties for some of the songs? I know that Over the Hills... is considered difficult, Stairway to Heaven is intermediate, but what are some challenging songs that I could learn?

Secondary requirement is that they have decent tabs, but I could always ask one of my friends who loves LZ much more than I do.
#2
I don't think Zep tunes are that hard, but they are challenging.
I think for moderate difficulty - try Heartbreaker.
For something difficult, try Archilles Last Stand.
Getting the timing and feel for the solos is difficult at times, cause Page played with a lot of individuality. The solo section of Heartbreaker is totally off the cuff.
#3
the solos are generally pretty hard to nail, so unless it's something like stairway, i'd just improvise.
rhythm-wise, you just have to listen to the songs to make sure you're getting it right, but they're not all that difficult.
#4
Alright, thanks! I'll probably start with Heartbreaker and work my way up.