Normally those app by Apple will be around 200 - 300 Mb each so it won't take much. Other apps most likely will be around 50 - 100 Mb, depends on the functionality. Simple app, smaller size. What really going to fill those space are mp3s, games like need for speed or infinity blade which can go up to 1 - 2 Gb in size and don't forget movies if you load them up in VLC or iTunes or any video players.
32Gb would be suffice for you if you know how to manage the space given. I'm the type that throws everything inside my iPad so even my 128Gb does not seem to be enough. It's full with vacation pictures, games and movies for traveling needs.
In the end, it's how you manage the space that's important. Some can make do with just 16Gb but I'm more to the bigger the better type. I'll never know when I might be needing the free space.
Sure now people says theres' the cloud where you can store everything but sometime you just need it right there and then. You don't want to wait for it to download from the cloud before you can start anything and then wait again for it to be uploaded back to the cloud right? If your iPad if the wifi version, then you need wifi for the cloud to work. And if you have the LTE version, you'll worry that your data quota going down the drain. So for me, space is important.
Ask yourself, is 32Gb enough, provided budget is not an issue.
Im using the 32gb, space is not really a concern for me as i throw all my pics in dropbox. The only game im playing is Clash of Clans and also The Walking Dead, so games dun take up alot of space.
BTW the Siege Glastimate tempered glass for iPad Air is reaching me on Monday. Let me know if u are interested.