:: Thanks for pitching in. I don't know a lot about these different padding schemes, so I'll have to read up. Right now the only comment I have is that it is possibly confusing mentioning Cramer-Shoup amid those padding schemes. I will think about a better way to mention both alternatives (padding scheme; CCA schemes "based on" ElGamal). 
 :: As for the citation about one-wayness if CDH holds, I'll look around for one, but the proof is so simple probably no one has bothered putting it in a paper ;) Suppose ElGamal is not one way (I have an adversary that inverts random ElGamal encryptions with noticeable probability), then I will construct an algorithm for CDH (with the same noticeable success probability). I get  as input, I pick a random  from the group, and give the adversary  as the public key, and  as the ciphertext. It responds with some purported message , and I output  as my purported CDH answer. With noticeable probability, the adversary's response  is the correct decryption of the ciphertext (i.e, it is such that ), so my CDH output is correct with the same probability. After this, I can use the random self-reduction of CDH/DDH to boost my CDH algorithm's correctness probability to very close to 1. 
 :: I don't think wikipedia is necessarily the best place for these kind of proofs. But maybe I can add it to the wiki site that includes the proof of CPA (that you just added the link to), if I can't find a reference elsewhere.