Is it untouched?
Generally it really depends on how far you want to go but assuming you keep all the watch together.....then its CG, Pin and rebrush, Remove AR, Lume it. You could also rebrush case if you want to go that far. I wouldnt to be honest spend anymore on it as if you want to make it better its not worth the hassle or money and to be honest you would end up with little of the original watch left if at all!!!
The best way of creating an ultimate is gathering the best parts and building it. ELs vary in versions so you pick the better parts from each.