I normally use a ton of addons, usually with an ElvUI base and then some essentials (WeakAuras, Skada, DBM), typically some "nice to have" (cooldown tracker, rotation helpers, Clique) and then QoL addons (auction house addons, fishing addons, rare finding).
When I tried to see how much of the default UI I could use, I still ended up with about 10 addons or so counting essentials like WeakAuras, things like Raven because the default buffs/debuffs suck, a chat addon and QoL addons like one to auto-repair and auto-sell gray items. IMO things like bag sorting, auto-repair and auto-selling should be baked into the default UI, along with a more intuitive keybinding interface.