1] There are many excellent mefarshim and seforim on Hilchos Niddah. In terms of those that are most popular, the Chavos Da'as and Sidrei Taharah are very well-known commentaries on Shulchan Aruch, although even those learning be'iyun would probably not be able to learn all of them in order. Many would also say that Aruch Hashulchan is pretty much a "must read".
As for more recent sefarim, there are many, many good ones. On my shelf (not that I've learned through all of them), you can find Badei Hashulchan (which is on Shulchan Aruch), Rabbi Eider's and Rabbi Soblofsky's English books (both of which are impeccably sourced and provide lomdus as well as practical rulings), and quite a few others. If you are interested in Sefardi Psak (and possibly even if you aren't), Rav Ovadia's Taharas Habayis is a must-have.
2] I would recommend looking for shiurim from Semicha programs. You can find quite a few sets on YUTorah, and I also know that Rabbi Weiner's shiurim (linked here) are excellent.
Note: I would also recommend that you speak to your Rav (or sign up for some sort of Semicha program, and speak to a Rav there) who will probably be able to guide you in these matters far better than I can, especially if you are interested in actually paskening these shailos and/or doing shimush in mar'os.