in which order should i start creating my map / objects / graphics

in which order should i start creating my map / objects / graphics

for example
i want to create a big map so would i first begin by creating a small version of my map so i can iron out the type of lighting / graphics i want or do i worry about that later? im worried it would take too long to bake lighting onto an enormous map later on?

 

My best suggestion would be to not overthink it (in most types of games it's the content/gameplay that matters more, i'd start worrying about this first ;-) ).
Apart from that, larger games typically start with a so called greybox prototype, meaning you mostly use boxes or basic shapes to define your level before actually building it. Maybe this is appropriate for your type of environment too. But depending on how far you are with your design/idea you may very well skip this step.
Behcause you wrote enormous map, my suggestion would be not to bake lighting but to use lightprobes (and maybe very low res realtime GI). This allows you to iterate faster. Eastshade is a good example of a recent (open-world-ish) game that mainly uses realtime lighting.