well ciasteczko is neuter so ciasteczka are plural neuter, (but yes accusative)
but for everything other than declension and sometimes numerals all neuter, feminine and masculine not personal nouns act the same way , you may see this in grammar tables as "not masculine personal", or "other"
also ciasteczka = plural nominative=plural accusative= plural vocative= singular genitive - usual for neuter nouns ending -o
I'd have to see the specific example, but technically the literal translation of "men" are "mężczyźni". "ludzie" are "people", but in some contexts this can be said by using "men".
Frankly, "nasi ludzie" sounds a lot more probable than "nasi mężczyźni", even if the English was "our men".
Biscuits, at least in UK usage, are different from cakes: twice baked (their name implies), flat and crisp, while a cake is soft, has been cooked with a raising agent. I'm not sure that 'cookies' in US English makes this distinction! Cakes are like 'buns', can be small, as in 'cupcakes'. Perhaps I just need to think in US English!
I do struggle with the pronouns more than anything because English does'nt have it which I'm not sure is a good or bad thing, I guess it is what we are used to. I also struggle with masculine feminine and neuter words as well, like mężczyźni, mężczyźna and all the variants like mężczyźnami etc and when and where to use them.