My understanding of Indian history at the time is mostly tangential, from Baktrian/Indo-Greek and Diadoch stuff. For which, by the way, there is no good up to date overall work. Bophearachchi is, I hear, extraordinarily good and the cutting edge of modern scholarship, but his work is focused on numismatics, and it's also in French, which means I can't read it. So if you wanted to get a good overview on the modern state of things, either you have to know French, or you can get a much more basic understanding from the UNESCO History of Central Asia, Part II. (Which is ridiculously expensive for an American.) The updated version of Narain's The Indo-Greeks (if it's not the 2003 reprint, it's not worth your money) might also help, although Narain is a bit radical on his treatment of Demetrios Aniketos. Avoid Sidky, generally a poorly written narrative survey that doesn't trouble itself with most of what's going on in India, and avoid Tarn unless you've already read some of the other, more modern works on the subject, because he wrote off the basis of some forged coins and missing a few important pieces. Holt's Thundering Zeus is fantastic but it doesn't cover India at all, it's limited almost entirely to the two Diodotoi and a historiographical analysis of Baktrian studies.