Hi Csnow,
I understand your frustration! I think part of the problem is that beyond the architects of the exam, as well as those who have taken the Alpha or Beta exams, there aren't that many people who have actually experienced these exams and can authoritatively answer your question.
I myself have not even seen the new JNCIE-ENT exams and am just now in the process of familiarizing myself with the exam. Hopefully, as these exams are being rolled out and more candidates take the exams, we will have more folks who can provide answers to your queries.
Honestly, i can't answer your questions with 100% certitude, but I would think your two EX4200 devices should be enough. This would provide you the ability to perform Virtual Chassis and other Layer 2 services quite fine.