When diving with a wetsuit it's a good idea to keep your ballast distributed to ensure you have reasonable way out of wing failure at depth. This is usually achieved by having some of the ballast ditchable. How much exactly depends on many factors and in some situations 12lbs backplate might be the optimal choice, in some it might not. Most of us end up with multiple plates for different exposure suits, tanks, undergarments, fresh/salt water. You may want to wait with that purchase until you go through balanced rig lecture during your Essentials (I assume you take it from Don). As always with weighting, ultimate check belongs in water, so you may want to borrow one and try it out, before pulling a trigger. There's a big and friendly DIR community in Bay Area.
If I were to guess, I would say that 12lbs plate is probably a good choice for saltwater, drysuit diving with a single tank and thick undergarments, but not so much for thin wetsuit in tropics, and also too much for doubles in any situation.