Your phrase can't use an article, so use:
There is very heavy security around that building.
But often you will hear:
There is a very heavy security presence around that building.
where presence is a singular noun (definition 1).
Though in either case you can't really know what the "security" involves.
Yes, in principle, but not the examples you give.
You could say:
There was water, a puddle, on the floor.
It's a bit of an artificial example. But it is correct. Your example doesn't work. With apposition the sentence should "work" if you only use one of the nouns. So if I say "He lived in Paris, the capital of France" and I remove ...
We usually refer to a potion in the sense of a particular mixture made up by someone, rather than a generic substance like milk or wine. So you could say 'The witch drank some of the potion she had made'. (Of course, we can also say a wine to refer to a particular kind.)
It's possible that some of the quotations found by Google are using 'some potion' to ...
Because spending is, as you say, a non-count noun, I would not use it when referring to specific amounts of money (like $2,000 or $3,000). I would use a different word, for example:
The expenditures for things such as books and salaries are $2,000 and $3,000 respectively.
But in the given example sentence specific amounts were not listed, so "...