What are the breast forms you have made out of ? You might be able to use liquid latex (they sell it in skin tones) to go over the seam (and makeup over that) - just make sure that latex will not have an adverse effect on the material they're made out of.
Not sure what you mean by the hair poof. For this I would want a lace front wig, stub it, and attach a ponytail/braid onto the stub. There are great tutorials on here for how to do that.
I would not really trust a C-string, especially if you're tucking (and especially a hand-made one, no offence - I've just read reviews where they've fallen off someone and that person didn't notice until it was too late, talk about awkward). I'd just use a "bikini" style panty - you can even sew or glue the "straps" to the costume so they don't show - you could even cut the "straps" off and sew it to the inside of the skirt-thing on the front and back. The real costume might have panties just built-in, I don't know (I doubt they would have wanted to risk flashing the audience and having to do re-takes,
The actual costume had flat mid-calf boots with gold details on them.
What's your rib-cage measure ? Does the 34 band bra fit comfortably ? Is this bra top the actual costume piece or something going under it ?