Hi OP, there is a lot of good advice here. I know how you must feel about the CAC score, it's a shock to get a high one. After my latest I spent weeks walking around feeling like I could keel over at any minute.
I'm 59 and my CAC score was 1124 in April 2021. I've been on rosuvastatin/Crestore for many years but ate an unhealthy Standard American Diet and had a high-stress job. Since late 2018 I have been eating a low-carb, healthy fat diet, and have sustained a 50 lb. weight loss on a husky 5'7" frame, I'm 175 lbs. I walk 3-5 miles a day, briskly, and do tension band exercises every other day. I'm semi-retired (part-time jobs).
Whether you eat plant-based, LCHF or Keto, I think it's important to avoid processed carbs and added sugar, they lead to metabolic syndrome which ties to heart disease. You want to be insulin sensitive. All of these ways of eating can help you achieve a good triglycerides/HDL ratio (ideally less than 1.5 if calculated using mg/dl measurements).
Something to keep in mind is that statins may be linked to elevated CAC scores.
Also, I have heard K2 works best with sufficient magnesium (I supplement).
You may want to check out Yuri Granik's high CAC score Facebook group, it's where I learn a lot of this stuff (private group, you have to apply to membership and provide your test scores).
And - lastly - high cholesterol is not itself necessarily bad, nor is high LDL. It's the type of LDL (either fluffy buoyant or hard and dense, the latter being the bad type). That can be changed by diet and lifestyle. I recommend you get an advanced lipid panel with NMR fractionation, it will tell you more about the makeup of your blood lipids and better help you assess your risk.
Stay well..