... I've been waiting for over 30 minutes, ...
Tamura uses "have been"+verb-ing because he is describing an action which started in the past and is still continuing now.
Other examples:
I've been working for Kobe Steel for 3 years.
I've been playing soccer since age 10.
Sorry, but this knife is dirty.
This expression is used to introduce some bad news. In this situation, Tamura is using it to politely complain that his knife is dirty.
Other examples:
Sorry, but could you turn the music down please? I have a headache.
Sorry, but I'd like to exchange this sweater for another. It's too big.
Could you bring me another one?
"Could you" + infinitive is used in this expression to make a polite request. You can use "can you" in the same way, but "could you" is more polite.
Other examples are:
Could you repeat that, please?
Could you fill in the membership form, please?
I'm afraid the music is a little too loud.
This expression is used to introduce some bad news. In this situation, Tamura is using it to politely complain that he wants the music turned down.
Other examples:
I'm afraid I won't be able to come to the party.
I'm afraid I can't help you.