just remember the SSD is the only thing you can upgrade later. I would not go with less than 8GB RAM these days.
the CPU power from weakest to most powerful when it comes to CPU's near the same speed (Speed in GHz., and this is for Mac Computers or otherwise anything) are as follows
Intel m3 dual core
Intel i5 dual core
Intel i7 dual core
the exception is sometimes a quad core i7 will be more powerful with a lower GHz clock speed than a dual core i7 that runs at a faster speed. They are for 3D CAD/CAM/Animation work, HD video editing, Hi-Res photo retouching, print/layout work, and gaming, though more gaming is done on the Graphics Processing Unit (GPU) and that's games that like to push the limit on action - again available on higher end macs not on the lower end ones, but if you just need to surf, listen to music, do homework any newer mac will be fine. Keep in mind the touch bar on the new mac is only compatible with software that makes itself compatible with it. So while most if not all new Apple made software does some other 3rd party stuff may not.
The MBAir is now about 2/3 years old with the only HW change being more base RAM (comes with 8GB not upgradable) so it's an older system but you can still find them for about $1K US, for $300 more you can get a lot more power out of Macbook or Macbook Pro, the Macbooks are generally lighter and come in more colors, the pros come in gray or dark gray, a bit more power. Lower end macs are designed more for battery life than power these days.
