2. Amplifier: The iPod Classic is actually quite good, a lot of third party boutique headphone amplifiers (at any price) actually measure worse than the iPod Classic or the last gen iPhones.
3. Source: The iPod classic is also quite good here to, a lot of boutique gear is actually more expensive but worse than the iPod.
4. The mixing and the mastering of your music is a lot more important than the format, without killer samples (which are quite rare in real music), I know very very few audiophiles able to distinguish between MP3 V0, > 220 kbps AAC or Vorbis and the original file. Anything superior to 16/44 is likely to be a waste of disk space, the difference between 16/44 is likely to be a different mastering or simply expectation bias.
Since you are a newcomer, welcome to Head-Fi and be careful of not succumbing to sanke oil based on bad physics and FOTMs.
(Flavor of the month: a new product that is backed up by publicity and enthusiasm but not real performance).