https://nursing.uth.edu/prospstudent/BSN/HESI.htm
^That link above should contain all the info you need about the HESI. Only five sections are required (A&P, Vocab, Grammar, Reading, Math) and the other sections (e.g. Biology and Chemistry) are not required and will not be looked at if you do them. ("The other sections such as Biology, Chemistry, Critical Thinking, Learning Styles, and Physics are not required and will not be reviewed.") I registered through Elsevier using the registration instructions in that link above and took it at a physical testing center, so I'm not sure how the Prometric registration process looks like. I do know that since I registered using the UTHealth code, my scores will automatically be sent to them (at the end of the month that I took the test). As for study materials, I used HESI A2 SECRETS and the Admission Assessment Exam Review E4 (I found the online practice exams it came with to be helpful) and studied about maybe an hour a day 3 weeks out? I ended up with a 96 composite (100 Math/A&P; 94 Reading/Vocab; 92 Grammar) and don't plan on retaking it. For those who are familiar with the TEAS, I found it easier. Best of luck!
As for CPR, immunizations, etc. I attended a webinar and the faculty recommend *not* taking any of those actions until you are formally/conditionally accepted since those actions may have time frames/costs associated with them. I could be wrong and I don't know anything else about immunizations, but I know that I won't start any of those until I receive my admissions outcome.