Are there certain badge acquiring strategies to follow?

No, that wasn't a mistake. Badges levels are cumulative, so a black badge counts also as a bronze, silver and gold badge in terms of requirements. Also, badges gained early still count for the requirements of later levels.

This is better explained by this image:

As you can see those two black badges will still count all the way through level 16, so you'd only need 2 more platinum badges and three gold badges to meet the requirements to get to level cap.

This lets you use any strategy you prefer. You can even concentrate on a badge at a time, knowing that your progress is "saved" for later levels.

From my observations I can say that usually people at levels 1-8 struggle to get the AP (obviously), once they get to lvl 8 it's the badge hunting till level 12 or so, and then it's again the AP that's missing for level 12-16

Given this, your strategy will depend on you long-term goals. If you don't want to get higher than 12 then ideally you should focus on badges from the first day on, the AP will follow automatically. If you want to get to level 16, then focus on getting as much AP as possible from the first day on, by the time you have the AP required for higher levels you will also have the necessary badges automatically.