I do think the power limit of the MBA vs the MBP will not be a factor in what you do.
Unless you need to do heavy 3D composition, audio or video the MBP would be fancy but not necessary.
Storage can be defined as your desk and all the drawers and papers
memory is the desktop
The more you need to take out of the drawer the bigger the desktop is going to need to be able to fit.
when you are not using these programs they can stay in storage and not need to be brought to that 'desktop'. the moment you open them they begin to use more RAM
What has happened is that as software becomes more sophisticated it requires more Memory to run, when the computer reaches that limit it looks to the hard drive for memory which will slow the computer down noticeably.
Memory (RAM) is going to be faster than storage on a sold state drive (SSD) - which is still a hard drive, just upgraded technology which is a lot faster.
You cannot change the size of the internal solid state drive (SSD) storage on most if not all new macs but you can buy external storage:
You can buy 200GB of cloud storage from Apple for $3 a month, you could get a network storage device for your home, an external hard drive or a combination of any of these
but while you also cannot change the amount of Memory (RAM) in the laptop, and there is no other solution to that like their is with the hard drive or SSD storage