What are the minimum and recommended hardware requirements for Xcode development on OS X?
Being a programmer myself, I think screen size and amount of memory are the most important factors to consider. The processors and graphic chips of all current MacBooks will be sufficient for this kind of work, although the MacBook Airs come standard with an Intel i5 processor, which can be upgraded to an i7 for a small price.

Memory: MacBook Airs come standard with 4 GB, which I think is not enough. They all have the option to upgrade to 8 GB though. The 13" MacBook Pros come with 8 GB standard, with 16 GB as an option. The 15" MacBook Pros have 16 GB standard.

For screen size, I like to have lots of it to do development work. Unfortunately, Apple stopped selling 17" laptops some years ago. On the other hand, almost all MacBook Pros now come with a Retina display, which means they have a much higher resolution for the same screen size. If you are comfortable working with smaller font sizes, you can switch to a "more space" option in the display settings, which gives you lots of screen real estate. You can choose between 13" and 15" MacBook Pros, but the 15" models are Apple's top of the line, so they might be costlier than what you're looking for. The MacBook Airs don't have Retina displays, and they come in 11" and 13" models.

A last point to look out for is disk size. All MacBooks, except for the 13" MacBook Pro without Retina display, come with an SSD. But with the cheaper models it's just 128 GB. On all MacBook Air models you have the option to pick up to 512 GB, and up to 1 TB on the MacBook Pros.

I suggest you go to the online Apple store for your country, and customize a MacBook Air or MacBook Pro to your liking and within your budget. Welcome to the Apple development world!