1. I wouldn't want to see IGA at the helm; he had a dozen chances already and I think he's really reached the top he can do with the formula he can do well (the Metroidvanias) while at the same time showing he's borderline disasterous at anything new.
I'd honestly take some new talent to the stage. Konami is bound to have young producers willing to prove themselves, and a 3DS title should be cheap enough to act as the stepping stone for such talent.
2. I wouldn't mind Michiru Yamane at the helm of the music, or just any of the old composers. I'd want some musical continuity in the sidescrolling titles (sidescrollers don't need nor support dramatic music). I'd love them to use the more powerful hardware to give us better sound-quality remixes of old tracks, and some catchy new stuff.
3. I'd definitely not want Kojima back for the artwork side of things; I really like her style - as long as it's not applied to Castlevania. I'd love a bold new direction for the artwork, in the vein of the many innovative 2D titles of the last years, or as something completely new, but it should definitely look DIFFERENT. Really different. Big sprites, quality backgrounds and all that. Fluid animation with tons of hand drawn sprites and the like.
In all honesty, I think the natural home of the next sidescrolling CV is XBLA/PSN; an HD CV title with a DS price tag (around 40$) in full 2D glory. A man can dream.