You have several questions here. Let's see if we can tackle them one by one.
"Several" and "multiple" both mean two or more. Either is acceptable here, and in context I think they would mean the same thing. Maybe, possibly, "several" would tend to make people think of a small number, 2 or 3 or 4; while "multiple" could imply a larger number. At some point we'd say "many" or some other word clearly indicating a large number.
An adverb usually comes after the verb it modifies, so "can even" is more common and "normal" than "even can". But both are acceptable.
"Labels and variables" is trickier. It really depends on what the reader is likely to assume. I'd say that the concept, the idea of a name/value pair, is a variable. It then has a name and a value. So I'd say "multiple variables", or "multiple name/value pairs", or "label/value pairs" if you prefer. If the reader can be expected to understand that every variable has a name and a value, or if you've already explained this, then you don't need to spell this out. I often write simply "multiple variables". If this could be confusing, if the reader might think that "multiple variables" means that you are just going to give a list of variable names, then yes, say "name/value pairs". Or explain it more fully, like, "pairs of names and values separated by an equal sign", or "a string of variable assignments, each given as a name, an equal sign, and a value, terminated by a semi-colon". Or however much explanation is appropriate in context.