2) What's with the "blech"? Is that a means of reminding folks not to use the burner, or a way of using the burner that stays within the "no work on Sabbath" rule?
I'm not Jewish, but I think it's referring to the requirement that meat and dairy products never be allowed to contact each other. Once a bowl or plate has been used to hold meat products, some form of cleansing is required before it can hold dairy products. During passover, the rules are stricter than during the rest of the year. My interpretation of the text from the manual would be that it's possible to clean the glass surface in a manner that satisfies the requirements for most of the year, but not during passover.
Perhaps someone can correct me if I'm wrong, but what I think that means in practice is that if you never use burner 1 for dairy products, and never use burner 2 for meat products, and burners 3-4 you would sometimes use for meat and sometimes for dairy, then during most of the year you can use burners 3-4 for meat or dairy provided they are properly cleaned when switching uses; during passover, however, you would be limited to using burner 1 for non-dairy products and burner 2 for non-meat products. Since burners 3-4 would potentially have trace amounts of both meat and dairy products, even though those amounts would be irrelevant most of the year, those burners could not be used at all during passover.
I may be misunderstanding the rules, however; it's possible that they would merely require that those burners be restricted to items that are parve (not meat nor dairy, e.g. vegetables) or require that once a burner is used for meat or dairy during passover it cannot be used for the other at any time during the season.
All very tricky.