Agreement

Hi,

http://www.guardian.co.uk/education/2009/aug/20/private-schools-pupils-top-alevels

The competition for entry to degree courses this autumn is unprecedented after ministers capped student numbers to avoid a budget deficit despite a 10% surge in applications.

1. Why is it "numbers" and not "number"? Isn't there only one number?

Up to 135,000 candidates were still battling to secure a place today – nearly 30,000 more than the same point last year. But the numbers available in clearing, the system used to allocate leftover places, is estimated to have halved to 22,000.

2. Again, why "numbers" but not "number"? Also, is there a subject-verb agreement problem here?

Linguists expressed concerns about the decline in students taking French and German, though Spanish entries were up.

The competition for entry to degree courses this autumn is unprecedented after ministers capped student numbers to avoid a budget deficit despite a 10% surge in applications.

3. Can I use "concern" instead of "concerns"? I never know when to pluralise this word.

4. Why is the plural form used in "Spanish entries were up" and the uncountable form in "the competition for entry"?

Thanks in advance