There is a Dr. Greger whose speech I can't stand but from whose books and online videos I have learned a lot (search for nutritionfacts and How Not To Die. Also, there are many, free online courses on health topics like the microbiome, epigenetics, diseases, nutrition, etc. that you can take through the years as they keep getting updated with the latest learnings (currently in vogue is the role of the microbiota in the gut, for example, so every few months new information is made available). What I've learned is that the human body is incredibly resilient and you can live several decades without major problems on the worst of diets, it's the accumulation of stuff over time that leads to what are now called Lifestyle Diseases and the ones it sounds you are concerned about: cancer, Alzheimer's, diabetes, etc.
Since we now know the body is an ecosystem consisting of smaller ecosystems and embedded in larger ecosystems, the interactions are too varied for anyone to predict what the best thing for you to do is. Statistics and studies only apply to large groups and always have outliers anyway. Some basic trends are useful, however, so you can look at which general lifestyles tend to produce fewer problems: moderate exercise, low intake of animal protein, lots of fresh vegetables, legumes, and nuts lead to healthier lives. Your best bet is to support what evolution has already solved for you and understand human activities and lifestyles through history (not the last several thousand years, mind you) and see how you can reproduce the conditions to which human bodies adapted to within the confines of modernity. Really, exercise seems to be the single most potent and underutilized method of becoming and remaining healthy, so kudos on asking for advise.
I one last ramble: supplements are only necessary when you have identified a specific deficiency and you can't address it through your daily nutrition. Vitamin D3 comes to mind if you live away from the equator and don't eat fish skin.