Are there any good, modern commentaries on Sifra (Torat Kohanim)? I am specifically asking for modern commentaries - I have mediaeval commentaries (like that of the Raavad), but I want something more recent. Doesn't need to be academic; just explanatory. Can be Hebrew or English.
I completely agree with @YK's comment, the Malbim is a great commentary on Sifra. I believe he had already written on some of Nach, but his commentary on Vayikra was the first sefer of Chumash that he wrote on.
At the beginning is the Ayelet Hashachar, which he recommends you skip on your first time. In it, he lists 613 rules of grammar and drash. Then on each "paragraph" of Sifra (he uses his own divisions which are not always the same as the typical perek/parsha + mishna divisions), he uses those rules to describe how the midrash comes directly from some feature of the words of the pasuk.
On Vayikra he wrote in this style for the entire sefer, including the aggadeta parts like the beginning of Bechukotai. On Shemot, Bamidbar, and Devarim, he only covered the Mechilta/Sifri for the halachic parts, and did his own thing for the aggadeta.
A minor detail - the Malbim does not cover the introduction to Sifra (Rabbi Yishmael Omer and a few more braitot explaining it), and my Malbim chumash doesn't even print it. You may want to go through that from somewhere else before you start.
It's an ambitious project, but very rewarding. (Actually, after 4 pesukim the Malbim realized that his original plan was too ambitious even for him, and scaled it down a bit.)