your going to need 6grams or more vit C daily, ideally as much as you can handle 10grams at least with your history. 2000mg a day for someone with your history likely wont do anything. You also want to take lysine and proline. I would also warn against using ester C because its ascrobate bound to calcium and nmost people dont get proper nutrients (like A, D and K) for the body to properly use all that calcium and you end up calcifying soft tissue, like arteries.
For niacin, try working up to 1 gram 3 times a day (3 grams total) this will help dilate blood vessels and unclump red blood cells promoting blood flow. Have to work up slow or flush will be too intense.
cyanocobalamin is nearly worthless for most people. Ideally you want methylcobalamin, I have found source naturals to be the best I have tried, must take it sublingually, let dissolve between cheek and gum or you will only get a fraction of what is in tablet. I personally use 10mg a day.
Make sure to get folate as well in the form of methylfolate, not folic acid, this goes hand in hand with b12, Solgar brand has been good to me.