Shopping for 1st/2nd hand CDs/DVDs/magazines

Hi

Planning to stock up on Japanese pop culture goodness while I visit Japan in April. I will be travelling to Hiroshima and Takamatsu, but I plan to leave my shopping at the final leg at Tokyo (unless if there's anything exclusive in those two cities). I have some questions, hope you can help out:-

1. In general, is Amazon that much cheaper than the main chain stores (Tsutaya, HMV, Tower Records) for NEW music releases? I know that I can order from Amazon in advance and then collect it at the hotel/nearby convenience store when I arrive to Japan, and I also know for some releases there are in-store exclusive bonus items. But I can imagine spending some time at CD stores to sample music, and I want to try to avoid going on a frenzy and bleeding my wallet dry......

2. Can anyone recommend any second-hand CD and DVD stores with a generous stock? I heard Disk Union Shinjuku is a must visit, are there any other places worth checking out?

3. I will be accompanying some friends to Akihabara, but for me it will be more of a weird-and-wonderful tour rather than shopping for idols/manga/anime/gaming. Since it's still a notable pop culture destination, will I be able to find 1st/2nd hand CD/DVD stores?

4. Aside from Amazon, where can I find back issue or second hand men's fashion/men's interest/women's fashion magazines?

We typically visit the Book Off stores for 2nd hand books, CDs and DVDs. They are almost everywhere, but it is worth visiting the larger ones; to give you an impression, this is just one aisle in Book Off Ikebukuro: http://monochrome.me.uk/blog/book%C2%B7off-ikebukuro/