There can be a number of things, did you check the brave FAQs to see why you possibly are not seeing ads? https://support.brave.com/hc/en-us/articles/360026361072-Brave-Ads-FAQ
Have you received ads in the past or did you just start using brave? Sometimes you also will just not see ads. I have not received ads on my mobil brave for a good few days now, same with Windows 10. Linux I received like three yesterday. And this is using the browser for a good at least 10 hours.
Not entirely sure, but you received an ad meaning it is indeed working. As the FAQ says sometimes you will go a day and not see ads and this is normal. You can also check what ads are available in your region checking this. https://sampson.codes/brave/ads/my_region/
Also it should be noted as well as that FAQ says, you are not guaranteed 5 ads in an hour if you have 5 ads displayed for the max. That just means you will max out on 5 ads in an hour if you receive 5. As I said I go hours and do not receive ads. But I believe it will be resolved sooner than later and I will eventually see ads again. I know they are working because I did the tester they have that sends you a test confirmation for ads to verifiy your device is set up properly to receive them.
No problem. I actually just received an ad myself on Linux. Not holding out for more, lol, just trying to be realistic here. You can also receive new tab page ads as well, however, I am not sure if it will payout in your region. But you can try. If you do receive them you can only get 20 in a day 4x in an hour. You can see more but you only get paid for 4 in an hour. And it is indeed a 24 hour based thing, so if your new tab ad started lets say 9:43am if you try it again at 9:41 the next day it will not payout. Most of my BAT this month has solely been through new tab pages because like I said, this month has not been a steady source of receiving normal ads.