Macbook Air purchase questions

Hi all

I am planning to buy a 13" 256 GB macbook air, and then retroactively upgrading the RAM and storage to 8GB, 512GB respectively. Now, I have a macbook air, which i got fro my workplace, and it is an early 2015 (7,2) model. I was looking up upgrade guides for the newer macbook airs, but only able to find upgrade guides, and parts for older models (upto 5,2).

The Ask :

Can anyone here guide me, on whether it would make financial sense to buy one of the lower models, and then upgrade the parts? I might even go in for the i7 2.2GHz model, if memory and storage upgrades are possible.

All help will be appreciated.