I would take the 2019. You get True Tone plus with the education store you get free beats studio worth £250 (either keep it and enjoy or sell them bringing the price below the refurb.
With regards to the iMac, what size 21 or 27? It will probably be slightly less powerful but have an ssd which makes the machine feel much nippier
Yeh wouod sell the Beats so maybe get £100+ back as market flooding with them think.
It's a 21.5" slim one. A concern maybe is it has a 1Tb fusion and Air Base is 128Gb so would have to use external or NAS? for photo library