I hate to be this person, but I will anyway, you’re going for a highly sought after role, where only 1-3% of applicants reach this stage. You are up against exceptional people.
The psychometric stage wasn’t competitive, it was essentially you against yourself. The DMI on the other hand is your time to shine, if you really want it, you will scour the internet and the forums, and obtain whatever resources are out there to help you prepare.
I understand I’ve not answered your questions, but many have poured hours, days and weeks into preparing themselves for every stage of this process. I would strongly suggest you do the same.