A: Yes, absolutely. All your EZdrummer EZX and older SDX libraries are fully compatible with SD3. This instantly expands your sound palette to thousands of additional drum sounds.
One of the primary reasons the SD3 core basic sound library is better for many users is efficiency. A complete installation requires over 230 GB of space, but the "Basic" tier provides the essential drum hits and core microphones in roughly 40-41 GB. On both Win and OSX, this version includes all the fundamental close mics, overheads, and the primary room mics needed for a world-class mix without clogging your SSD with surround channels you may never use. A: Yes, absolutely