Ah yes, I mean, by planning I include prototyping to see if the idea clicks and ultimately works well within a period of a jam xD
Anyway, the way my bullet pattern system works is pretty simple - There's a scriptable object that works as a template for all the features of a standard bullet hell pattern, as you can see:
I took heavy inspiration from this video:
But also made my own quirks like accuracy (which 1 means its totally accurate and 0 a random value within the specified local angles) and burst (which I actually took inspiration from the Unity's particle system which shoots a specified number of bullets then waits for the end of its duration to shoot the burst again).
The bullet's speed is actually defined within their own prefabs, along with other settings.
There's also support for multiple patterns at the same time, it's how the boss patterns work, a double spiral of small bullets and a circle burst of big bullets.
This system allows me to reproduce most bullet hell patterns in bullet hell games, but there's still some limitations because I haven't polished it properly, like acceleration and stuff like that isn't supported yet.
If you'd like, I can share you the source code of the game if you'd like to take a peek, but I still have to do some code cleaning xD