I have an iPad 4th gen and it is NOT the same as the Airs.
It can handle most apps I’ve tried OK, but running multiple music apps at a time starts to bog it down pretty fast. It really depends on the specific apps though. Sometimes can get away with 2 or 3.
Also be aware that after they released the 4th gen, they came out with the 4th gen MINI, which was the crossover point to a new type of processor. Gradually, and even more recently, there have been an increasing number of music apps that require at least the 4th gen MINI or higher, thus excluding the 4th gen standard.
Also a few requiring iOS 11+, and the 4th gen standard is maxed at 10, can’t upgrade to 11.
There is still a lot you can do with it in the music app world but you’ll notice the limitations mentioned above pretty fast. If at all possible, I would recommend going for something newer.
Oh and for field recording, it should be able to handle direct recording just fine but I wonder if it would be better to just get a portable recorder. With the iPad you’d need to either use its microphone or get some kind of attachment recorder, or use an audio interface… seems like more hassle than it’s worth when there are easier options.
ALSO!!! - @xidnpnlss mentioned that newer iPads at $350 USD (actually $329 if I remember right) - BUT, I just read something the other day that the next gen iPads are going to be $250, so it might be worth waiting to see how that plays out (EDIT to clarify for anyone else stumbling through this - Most recent iPad was just last month, March 2018 at $329, so this rumor of new $250 iPads definitely won’t be for at least many months, if at all).