Learn English – “row count” or “rows count” to mean “number of rows”

Yes, you can use "a good number of" in this way.

To distinguish the two meanings, it's necessary to rely on context. As a rule of thumb, the "many" meaning is generally used when what's being described is something that a person or thing has done, is doing, or will do:

• Over the years, he's made a good number of controversial statements.
• She's a good number of points ahead of the other players.
• He's set to appear in a good number of films over the next 5 years.

Whereas the "suitable or preferable quantity" meaning is used when either the suitable quantity or the good number is the subject of the sentence:

• [A good number of community service hours] ^SUBJ. to have would be around a hundred.

• [Less than 40 students] ^SUBJ. is a good number to have in a classroom.

However, while I can't think of any, there are likely to be exceptions to this rule of thumb, and you'll have to determine whether it makes more sense for the phrase to mean "many" or "suitable/preferable quantity."

They mean roughly the same thing, but I think they emphasize slightly different situations. "Permissible" is an adjective, and "is permitted" is a passive construction. The passive construction somewhat implies that there is some authority enforcing what is and is not allowed. In other words, I would expect "it is not permitted" to be used when someone will actually stop you from doing whatever "it" is. However, they do really mean the same thing, so they can be used interchangeably.

"Permissible" means "able to be allowed", and "permitted" means "allowed". Again, there is a slight difference in the literal definitions of the words, but they both describe the same situation. The fact of whether or not something is allowed is a permanent characteristic of the thing (unless the rules change). For example, if dogs are permitted (or permissible) inside a building, that fact is true before a dog comes in, while one is inside, and after it leaves. This is different from similar word pairs like "inflatable" and "inflated". An inflatable chair is always inflatable, but it is only inflated when there is air inside of it.