Underwear, like trousers or jeans, are referred to as a pair, because it's a throwback to when pants (pantaloons) originally came in two pieces - a matching pair. A person would put on one leg, tie it around their waist, then put on the other leg and do the same.
For more information, there is an excellent thread in EL&U, which references the following text:
Before the days of modern tailoring, such garments, whether underwear
or outerwear, were indeed made in two parts, one for each leg. The
pieces were put on each leg separately and then wrapped and tied or
belted at the waist (just like cowboys’ chaps). The plural usage
persisted out of habit even after the garments had become physically
one piece. However, a shirt was a single piece of cloth, so it was
always singular.
Pants have obviously evolved, but the terminology still remains.
Therefore, "how many pairs of underwear" is correct usage. For example:
How many pairs of underwear are you packing for the trip?
I'm bringing five pairs of underwear with me.
That being said however, in question form, we can use much, e.g.
How much underwear should I bring?
you should bring five pairs of underwear.
so much so
Use "so much so" for a quality like "amazing".
Use "so much" for a quantity e.g.:
He has a lot of talent, so much that he won first place in the competition last year.
Best Answer
Determiners are words like: a, the, this, that, my, your, no, one, two, many, much.
If a noun already has a determiner, we can't also use the determiners much or many with that noun:
We also cannot use much or many with pronouns:
When we want to use much or many with these phrases, we need to use a preposition phrase with the preposition of:
If the noun doesn't already have a determiner, we do not need to use the preposition of when we use the determiners much or many:
The Original Poster's example
In the Original Poster's example they use the uncountable noun administration without another determiner apart from much. Because of this the OP doesn't need to use the preposition of:
However, if they wanted to use another determiner with the noun administration, then they would have to use much of. Here are some examples with the determiner this:
Hope this is helpful!