I posted this elsewhere but my core is usually:
Stable/OS driver - speed 6-9, not utility beef...think Teebird
Stable/US driver - again speed 6-9, not super flippy...think Leopard
Stable/neutral mid - something that literally works on every line (Comet right now)
Stable/neutral putter - same as mid but a putter (Aviar, Magnet, Wizard etc.)
I try and rely on shot shaping more than having a specific disc for every shot and when that runs out, I will add something that can get the job done (Zone, RR, FB etc.)
I've more or less adopted something like this now. But looking back:
It's been trial and error for years. I can't say I had an established method of building my bag from the get go, like the Build-a-bag template. I just went through discs left and right, built a bag from one composition to another, tried minimalism, etc. However, I always built my bag higher than my rating/ability, if that makes sense (thinking a destroyer should be my max D, or that I need a OS Disc for every category, etc).
Now... I'm trying something different, cuz why not. I'm bagging discs that I've grown to really enjoy that fit together. Really, hand feel is a huge factor for me liking a Disc. So, I'm throwing Trespass', Undertakers, Truths, Judges. Can manipulate a lot of lines with those. However, I've squished the Enforcer/Stal into a Machete (no forging necessary) and keep a zone for short OS duties.
We will see...