1. Как-то нехорошо спрашивать: «вы тут ошиблись случайно или нарочно?», но попробую перефразировать.

2. Спрошу.

3. Уже спросил (по просьбе Димы Быстрова). Идея и реализация Викерса (он математик по образованию).

4. За исключением нескольких фрагментов, которые перешли из ZX81 и которые делал еще Джон Грант (например, поддержку принтера). Вот что говорил сам Викерс:

I did more for the Spectrum than just write the manual. I also wrote almost all the ROM code (in Z80 assembler). This was when working for a small firm called Nine Tiles Information Handling Ltd, who were contracted by Sinclair's to write the ROM code for the ZX80, ZX81 and Spectrum.

In more detail,

ZX80: ROM code written by John Grant, boss of Nine Tiles.

ZX81: ROM code put together by me (the greater part I wrote new, the rest adapted from ZX80 code). I also wrote the manual.

Spectrum: ROM code written almost entirely by me, and I also wrote the manual.

Ace: ROM code and manual by me, hardware by Richard Altwasser (who had worked on the Spectrum H/W at Sinclair's).