1. Yes to the first part, no to the second
2. Yes, for certain boards (explained below)
3. Depends on the saber. I honestly prefer low profile tactile switches more than any type of AV switch. Excited for a few builds coming up that are going to be using just tacts.
Short version: At least one momentary switch is required for sound sabers, only stunt sabers use just a latching switch.
Basically, the momentary switch sends a control signal to the sound board that causes it to do different things based on variables in the board settings. Short press for power on, hold for menu, etc.
Different boards have different requirements though. Every board needs a momentary switch for the Aux effects (blaster deflect, blade lockup, etc) and menu options. The NEC Spark Color 2 (the soundboard in the Hero tier) can be configured to use a latching switch for the Main switch (blade on/off) but the second switch still needs to be momentary. Any board that just uses a single switch has to have a momentary though (like the Plecter Labs Pico Crumble and Nano Biscotte, or the NEC Spark 2 setup for single-button operation).
Plecter Labs Crystal Shard, Prizm, and Crystal Focus boards all support momentary or latching for the main activation switch. The Ascend saber by Genesis Custom Sabers (using the CS3.0) even comes default with a latching slide switch for activation.