B12 is pretty necessary. Due to modern farming it's almost impossible to get from plants anymore.
As for the soy, I've heard good, bad, medium, never-touch-it, live-off-it... everything. The best thing I can say is 'everything in moderation, including moderation' (my family's motto). They say 25-30 grams of soy protein a day is good for you. The longest-living population is in Okinawa, Japan, where they average 2 servings of soy per day. That said, high soy levels may complicate certain medical conditions involving estrogen. But if you had that kind of condition you'd already know that.
As long as your protein is coming from a lot of sources (soy, other beans, legumes, nuts, seeds, dark greens, grains - pretty much every food has at least a little protein), then you should be fine. Eat too much too often of any one thing and you'll have issues.