i might add especially for F2P.. I use stamina potions for upgrade/awakening materials "only" during weekends because of the x2 reward and then weekdays do just elite instance. I think having all the events + daily missions + story missions is enough exp so no need to use it on monday (for x2 exp).. besides as a F2P u want to stay low level as possible while increasing your power, u can maybe go up to 70 (so u unlocked all treasure) or 80 (for reforge and to unlock all mystery) then level freeze there (event like matsuri match you up with around your level so it can help you even a bit)