My key advice for the BEMP exam is to manage your time during the exam. Since it is computer-based, it's easy to skip questions that might take longer to answer and come back to them later. So, answer the short or easy questions first to minimize the amount of questions you don't answer. I do remember running out of time and having to leave ~5 questions blank, so it was a bit difficult, but I luckily answered the remaining questions well enough to pass the exam the first time I took it.

Regarding studying, when I took the BEMP exam it focused more on the underlying principles of what each ASHRAE standard covers rather than the specific information/details of tables or requirements within the standard. ASHRAE does change the information that they test on, so you can also review Appendix A of the BEMP Candidate Guidebook to see the topics you can expect in the exam and their relative "weighting" of importance or how often questions focus on each topic. Furthermore, ASHRAE standards and other resources useful for preparing for the exam can be found here.

There was a similar Unmet Hours post here about being certified for OpenStudio modeling specifically, which does also mention the AEE Building Energy Simulation Analyst (BESA) certification as an alternative to the BEMP. However, this requires that you attend a seminar as well as pass an exam (BEMP only requires passing the exam).

Best of luck if you do decide to take the exam!

I used the the sample questions ASHRAE sells. Make sure to study all the different types of models and when to use them from the Energy Estimating and Modeling Methods section in ASHRAE Fundamentals.