Like others pointed out, there isn’t “the best approach”.
For an equalizer or actually for any plugin project there are certain domains:
UX: how is it used? how is information presented?
I was amazed when I first time worked with bx_digital where you audition an individual filter when auditioning. I guess many EQs have that nowadays
Sound quality: What filters are used? Is it phase linear? Any specific filter curve others don’t have?
E.g. most older EQs don’t have the “tilt filter” (if that is an official term, not an EQ expert)
Scalability: How many filters does it offer? Are you overwhelmed with too many filters?
Presets: Does it offer presets? Are they sounding any good out of the box? Are they well named so the user knows instantly which to choose from?
Personal touch: Is it a specific design? Does it appeal to certain users? Anything else that distinguishes from others
Any other power feature: Measure attenuation and auto-compensate? AI? Or whatever helper…
So it is really a question on what to focus and find trade-offs.
TL;DR: Start implementing whatever comes to mind, play with it and see if there are things you want to improve. An EQ is a good starting project and you can learn a lot.
If you are looking for a project to live from, I guess it would be hard to come up with an EQ that stands out nowadays.