2. The Tall pixie MTM will be too pale for the Juicy Couture doll head.
I do not think your doll look jarring to me. While the head and body is not an exact match, to me, it is close enough. The neck does not look too long either. Juicy Couture doll, like most Barbie Collector dolls of that era has a slightly smaller head.
Also, the legs of the MTM dolls are a bit shorter than Model Muse but I don't find it distractingly so. (How I wish Mattel would make a MTM with Model Muse proportions!)
Lastly, as someone who rebodies all the time, sometimes it is just not possible to find an exactly match even when you have a large collection of MTM bodies.
I think your doll looks very good. Maybe you should style it and dress it and live with the doll for a bit and then decide if you want to buy more MTM to rebody. Enjoy your new rebodied doll!