I've replaced my MacBookPro 17" with a top spec iMac 27" and was looking at a MacBookAir for mobile use but have held off because of a hunch that the iPad would get powerful enough by this generation to run desktop class apps. I wasn't wrong: iLife and iWork are now featured matched to the Mac, Logic has its companion app and Aperture is a good candidate for one as well. I think that an iPad Air can fulfill the role of a MacBookAir for most practical purposes.
So iPad Air it is for me. Friday!
In most cases those applications are very stripped down and don't compare to their desktop versions. I've already tried to do what you are planning and it just doesn't work that way with an iPad. iPad is a consumption device plain and simple. Apple can try to convince us otherwise, but for those of us that hoped and tried it just couldn't make it work well enough. There are even web sites like ADP's payroll web site that you just can't use because of the inability for it to scroll on the mobile browser... I could go on and on... Hopefully you don't do many of the things that I and many others do that has us now going back to Macbook Pro's and MacBook Airs so we can actually do some work.
The Air is great, but not for productivity!