Exactly, "het" can be one of the definite articles "het" or "de" (if it comes right before a noun) and it can mean "it", when the pronoun "it" is referring to either a very general "it" like in "It is cold" (Het is koud.) or when referring to an object that you know to be neuter.
I think the issue is the English there. Yes, your sentences are valid gramatically speaking but nobody says "It has been bread" or "What has been your food source?". Its not wrong, but it is clunky.
Instead people say "It is bread" or "it was bread" (if you want the past tense) and "what are you eating" or "what have you eaten"
It should be a regular s sound here. In Dutch only /sj/ as in for example "meisje" (girl) and "sjaal" (scarf) and sometimes /ch/ in loanwords like "chocolade" (chocolate) are pronounces as English /sh/. Sometimes when speaking fast words like "speciaal" (special) are pronounced with sh too, in IPA /speɪʃa:ɫ/. However, many Dutch speakers use a lower pitched /s/ that sounds somewhere in between English s and sh, but this is not the standard and happens mostly in some accents like in Amsterdam.