Yes doing the 2-1 quest costs 12 stamina and gives you chance for bonus stage which will give you 2 mayu... The chance is to get bonus stage or boss fight, so if you have a boss waiting in your raid area you get better chance for it to be bonus stage... the 50 stamina ones are bad stam per manyu so skip it till you get to 80 stamina bonus stage which is what 11-1 it starts giving those? not there yet myself.

Been doing 5-4 a lot myself as though the stam costs more to due that quest the exp ratio is greater per stamina used and to me seems better odds of bonus stage. note that 50 stam gardens start on stage 6-1 so... this can get repetitive...

Don't forget to do the lower level daily quests even if you don't want the dragon or such as the flower you get as reward can be used to rejeuve stamina or get girls...