grammar - で used for abstract location?

Consider the sentence:

今度の旅行は全部で何人行きますか。

I would roughly translate it literally to:

For this trip, in the domain of "total"(abstract location), how many people will be going?"

And then more naturally as:

How many people in total are going on this trip?

My conjecture: で is taking on the role of "location where a verb/event occurs".

(Question 1) What is the role of で for this type of usage?

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Other things for your consideration:

JMDict and WWWJDIC categorises 全部 as:

Adverbial Noun (副詞的名詞)(Q1.1),

noun (temporal) (jisoumeishi)(Q1.2)

(Q1.1) But I don't think 全部で acts adverbially to modify the verb　行く. Am I right? (Please correct me if I'm wrong)

(Q1.2) I don't think this part is relevant right? (Again please correct me if I'm wrong)

Answer

全部で

is an expression meaning "in total", and is strongly related to the fixed way to say "N of us went to X" (XにN人で行きました). Rather than an abstract location, it's closer to the "mean" で, the one you use to say "I went by car".

So, it's like "By what did you go there" (なにで行きましたか？), "By what number did you go there" (なんにんで行きましたか？), and so on.