I think everything you said sounds reasonable with a possible exception of the Nalimov tablebase comment (proven perfect play/result of any position with 7 pieces or less for those that are curious about the definition).
6 pieces. I just gave that as an example. A forced checkmate or conversion would also work. I wouldn't want to allow resignation if there's a realistic chance of drawing, put it that way.
Sounds good. We are basically in agreement.
Its not a big deal but it does look like 7 is now the correct answer. I do remember when it was 6:
http://chessok.com/?page_id=27966Endgame tablebases are computer databases of chess endings with precise calculations for optimal play in any position, provided the number of pieces on the board does nor exceed a certain limit. With Lomonosov Tablebases, this limit has gone up from 6 pieces to 7!
https://en.wikipedia.org/wiki/Endgame_tablebaseBy August 2012, tablebases had solved chess for every position with up to seven pieces (the positions with a lone king versus a king and five pieces were omitted because they were considered uninteresting).[1][2]