1. Any idea why "minus one (core)" when script threads are automatically assigned? Perhaps it's just being conservative to not impinge on other user functions?
The main thread is already being occupied by your Bitcoin Core instance. The -1 is used to account for that. Pegging it to the number of cores instead of the number of CPU threads partially accounts for the latter.
Further, I see that the chain state is stored in permanent memory, I'm assuming, when a block is finalized and added to the height, but that during processing, the chain state is cached in RAM, thus the benefit of increasing RAM to increase efficiency. Agree?
Chainstate gets flushed periodically during initial block download when it is filled. During processing, part of the chainstate can get cached in your RAM, which means that you're less dependent on your I/O speed since the RAM is way faster.