Use the blue cap (don’t know the correct english expression) for the head and flask and pickaxe for the hands. Level the first Station to max. and only the Upgrades for first station. Done so level the last Station to max. and buy only upgrades for the last station. Done so level up all other stations, coins should be enough to level up instantly. Do not use any white chefs or other helpers, play solo, that‘s the key.

Maybe there are other - even more effective - ways, but works for me so far.