I take a B complex in sublingual/liquid form once a week.  I believe one dose has 1200 mcg (20,000%) b12 and the other b vitamins in it are 100 to 300%.  My guess as to why the B12 dose is so high is that not all is absorbed.  It does seem a bit high but I havent had any trouble and I have taken it for over a year (I took this long before going vegan which has only been four months).  I also take a vegan DHA capsule that is derived from algae instead of fish and uses vegetable glycerin in the capsule instead of animal glycerin.  I had to do some searching and calling companies to find this DHA and confirm the ingredients are not animal derived.  I am in surgical menopause even though I am quite young due to losing my ovaries and the added omega 3 in addition to what I include in my diet (walnuts, avocado, flax oil etc) is very important for me to lubricate those joints etc.  Otherwise my only other supplements are a calcium/magnesium supplement (without D3 or other animal derived ingredients which was also no easy task to find as D3 is in everything grrr but I found a pure calcium supplement at GNC with no questionable ingredients ) and a D2 supplement I had to order online.  I take those because I have a severely low bone density (also had long before going vegan due to surgical menopause and years of low weight).  If I didnt have the health issues I have I probably wouldnt even bother with supplements because my diet is quite healthy and varied.  I also find it interesting that omnivores like to think vegans have to take supplements all the time due to lack of nutrition in their diet, but 99% of the supplements made out there are omnivore based (made with animal ingredients) such as fish oil or D3 that are so widely promoted, and the majority of omnivores that take supplements do so because of lack of nutrition in their diet (although in many parts of the world due to abuse of land/factory farming/pollution our plants do not have the mineral and vitamin content they once did so it is a concern for everyone).  I believe a vegan diet is much healthier for sure.  As I am fairly new at being vegan myself, I bought a book called "Becoming Vegan: The Complete Guide to Adopting a Healthy Plant Based Diet" by Brenda Davis, R.D. and Vesanto Melina, M.S., R.D. and this book is very comprehensive on vegan nutrition.  It even includes sections for seniors, those with eating disorders, teens, etc. and how to get optimal nutrition.  You might find it very helpful.  Hope this helps!  Good for you for taking this step!