Congrats on the new cage! I have the same one for my GCC and the space is amazing.
I can't comment much on the vitamins because I haven't done a lot of research into them. Though the general concensus is no, not required unless prescribed by a vet.
As for calcium/cuttlebones, as far as I was aware, they do not need it, though they can have them. I read a few places that cuttlebones were highly recommended back before it was widely known that a seed diet is not a sufficient diet for a bird. I also remember reading about birds like budgies & cockatiels, who tend to be fed more seed than other species (both because they're stubborn and won't eat pellets, or the owners don't know to feed pellets) need the calcium to aid in the digestion of seeds. Though I also recall this was to help break down unhusked seeds. I don't have any references for you because I ccan't remember where I read it, sorry.
But in any case, I don't think the cuttlebones are a necessity but I don't believe they will hurt. I know I've offered them to my baby in the past and she chewed the heck of it - mostly I believe to destroy it for fun (she flung it and chased it), but it's not there constantly. I keep up her calcium in other ways
*edit- please don't take what I said as gospel. I could be completely wrong, I'm no avian diet specialist
. More experienced people may come along and say I'm completely wrong, and that's Okay! Haha
