All I can say is that they are good mics, especially for the price. To clarify, I am not saying they are good for the money; I'm saying that I could easily spend a lot more money but not necessarily get better quality for extra money spent.
While you do indeed need a mixer, good used Mackies are everywhere. Don't know how many mics your kit would take,but I need 9 mic inputs for my kit, and many drummers only need 5 or 6. If you only need 5 or 6, you can get a Mackie 1402 series, which is smaller than a 16-channel I have, but more extra channels makes for more flexibility when you grow. I have their 16-Channel CR16series, which go for around $200 all day long. So, instead of buying just the Audix mics you were considering, you could get the KAM mics AND a mixer and maybe even have enough left over for mic cables. If you consider that you can stick with the headphones you already have, since you'd be mic'd, the cost of theSE15s could go toward a mic and mixer setup as well.
As far as software is concerned, you were initially only looking for a monitoring solution for practice, so recording software shouldn't be factored into your cost. Besides, Audacity, which is free, would do you just fine, if you just want to record yourself, but you do not need any software.
You can record full band setups, as well, with Audacity. What you can't do is adjust each track in the mix after the fact. But, after listening back to a few recordings, you'll learn which instruments need to be louder or softer and adjust their levels on your mixer. Once you have that dialed in, you can get some good full band recordings.