Translation:The cups are very small.
It appears that "muito" doesn't agree in number. Does this apply to all adverbs?
it applies when you translate "very" - it is always "muito".
So other adverbs agree in number?
No, since adverbs is connected to a verb, not a noun.
Bom ponto! (I hope that's right!). Obrigado!
I think "too small" should be accepted, don't you think?
You're right. Just report.