2) According to the official Blackout manual, the speech board was technically optional. So if you disconnect it, you (should) have sound without the speech. I'd test to confirm this but I've disassembled mine temporarily.
3) It's technically possible but you'll need to understand the exact memory parameters of the original speech roms. Today we think of "sounds" and "callouts" as individual sound files that are opened and played via a call from code. In classic pins, the "sounds" were generated by routine in the game code, and "speech" was compressed to exactly fit a specific memory footprint, and the game code would look up a specific byte. So it's doable... but in a different approach.
4) see #3: to redo a game with modern coding approaches, some people reinvent the wheel. Neither approach is "wrong" per se. It's all about your own comfort and resources. Either promises to be a learning experience.
5) Almost anything is fair game... it depends on what you want to do. Share your ideas! But if the original plastics are in decent shape I would preserve them, you might even be able to sell them. But trace their shapes on paper or clear plastic and go from there to draw out your own ideas...