looks like a nice little project and thats what it is all about trial to see what works.
u shouldnt need a cup over it now that its sprouted. i'd say 12/12 is best straight away for it will not grow out of control in your limited space.
i like the ash part, i used to put dried weed leaves on top of soil and i swear it improved the smell. have u thought of smell if this will be a problem for u.
its only the one so u should be right but maybe think of getting some sort of fan in there so it doesnt grow all spindly and snap on ya just when the buds are getting nice. they like a little stress.
u might want to try sum type of trimming so she keeps to the grow space, and so light gets to most leaves, ive seen a mate train his to grow around the space like a vine, another just grew one Big Bud. Dont over trim tho, do it gradually.
u shuld PM me sometime tell me how those lights work 4 ya ive been interested in em.