The amps are 150x4/50x2/500x1,Class AB. I've seen installs with more power than that which have activated the "excessive battery drain" warning in the E9x (I've tested some in my own E91). This system didn't trigger the draw warning, and we've done similar systems in M3, 335i, and 135i, all without issue over the longer haul.
As far as weight of the gear, the sub driver was 13 pounds (most of that is neodymium), the enclosure is 14, I will consider the upgraded tweeters, mids, and midbass speakers as a push, the aluminum amp rack is maybe 3 pounds, the wire was probably 15 pounds, and the amps themselves are roughly 10, 10, and 18, so between 80 and 85 pounds added. So, from a weight perspective, we added one Olsen twin (the thinner one).