as said it really depends on what you are trying to achieve and how detailed you want to go , your base material will determine what’s possible . better quality material will likely give better results , cheap cast parts that may have minor inclusions or inconsistent thicknesses could see you scrapping your project before you even get to paint .
you need to speak to those who do it on the daily basis for the best advice really . If you’ve seen some custom work then just ask who did it and take it from there .