I also use the 250ohm DT990Pros and am very happy with them. I have them paired with a $99 Atom Amp+. If you go with the lower ohm version I bet you could delay the amp purchase depending on the output of your computer's default stack.
For a mic I attach a wireless Antlion ModMic which is... Fine. Audio quality is good but it is kinda wiggly and charges off micro USB. Allegedly Q1 they're going to announce a revamped version which I think it really needs.
Regardless of which headphones you decide on, if you're interested in a budget headphone amp I can recommend the Atom Amp. It does everything I need with good build quality at an affordable price. I've used it for several years with no complaints
I loved ITSOL! Just reread it last month actually. I remember just being on the edge of my seat for the last third of the book If you enjoyed that I would recommend The Powder mage Trilogy by the same author, he does a good job of mixing a mystery investigation POV and a more action oriented one, just like in ITSOL, and I find it very engaging. Also The First Law Series. I think you'll enjoy the tone and mix of Known and Unknown Magics in those series similar to ITSOL.
I can also recommend The Will of The Many and The Blacktongue Thief, which were two of my books of the year for their releases, if you're looking for fantasy with a different tone than your standard, run of the mill sword and magic series