Azure Text-to-Speech Usage / Free Plan Credits

Hi, I'm new to Azure so please bear with me. The portal is incredibly confusing and overwhelming... I only just signed up a couple of days ago and I'm definitely more familiar with Google Cloud. Anyway...

Two questions:

(1) I've only used the Text-to-Speech service so far, both directly on the web in the Speech Studio, as well as via REST API. As mentioned, I only just signed up, so I'm on that "Free (F0)" plan, which means that I get 0.5m characters included per month (https://azure.microsoft.com/en-us/pricing/details/cognitive-services/speech-services/).

Where can I see how many of those 0.5 million characters I've used so far? I can't find anything, no matter how long I've already searched...

(2) Again, as I just signed up, I'm on the "Free (F0)" plan. I also got a $200 credit from Microsoft for signing up. So 2 sub-questions here:

a) I will most likely exceed the 0.5m characters that I got for free (see first question), so what happens then? Will I be charged and if yes, will that be deducted from that free credit I received? (again, I have no idea what my usage is, hence question 1 above...)

b) On that URL I linked above, there's also the "Pay as You Go: pay only for what you use." plan just below the "Free (F0)" details, where I can see that it's for TTS $16 per 1M characters. That's what I most likely need and want. How do I switch to this pay-as-you-go plan? What happens to my $200 credit in this case?

Apologies for these (maybe just newbie) questions, but it's seriously confusing. Thank you for your time.