Fast Song Switching is achieved by both Linked Racks (also known as Shared Racks) and Set List Pre-Loading
Linked Racks hold commonly used instruments and effects that are used in more than one song in a set list. This allows only one instance of each Rack with an instrument to be loaded in RAM for fast access when used in combination with the Set list pre-loader
The Set List Pre-Load function allows the entire set list of Songs to be loaded into RAM memory for fast Song switching during a live show. This is also aided by C3 Performers State switching inside the Songs for fast solo to rhythm instrument changes. The Linked Racks mentioned above also help save memory because without them the set list pre-loader would load multiple instances of all the Vst instruments used in the entire set list even if they were the same one and run out of RAM pretty quickly.
No, you can use all midi controllers with solo.
Yes, without Performer you can’t have the mirrored controller feedback used for rotary LED rings and slider strips that show current controller values and sync with sliders and knobs in Cantabile 3.
Complete Rig Control refers to the addition of flexible Trigger bindings for vst and outboard synth configuration, led feedback loops for external controllers to mirror C3 slider and knob settings and the MIDI clock external syncing capability.