I don't know what, specifically, the OU rep sent you. The URLs to the exam information for those three exams are at the bottom of this post. Apps certs are not my specialty -- I deal mostly with database and programming certifications. However, the fact that they are all 'Essentials' exams tells me that they have no exam or training pre-requisites and that they could be classified as 'basic' certifications. I do not believe that you will find 'levels' of certifications for these areas -- they tend to have 'Specialist' certifications (as these are) or none.
As for which to choose first? Pick one. There is no reason to choose one over another unless you personally have one.
Dumps are prohibited study materials and can cause you to be banned from the Oracle Certification program. Asking for them on the Oracle certification forum is extremely unwise.
Oracle EBS R12.1 Inventory Essentials
Oracle EBS R12.1 Purchasing Essentials
Oracle EBS R12.1 Order Management Essentials
Additionally, I recommend you visit our website certification.oracle.com to see what certifications are available. You will also get more info on what the requirements are for each certification, recommended training, exam topics and other exam details.
Good luck on your chosen path.
Certification Forum Moderator