Per Hedge, the total inventory space is around 750 slots, and is capped at 1000.
Theres around 100 red illusions in the game
Around 300 ish(?) cosmetics
131 frames
75 Blacksmiths templates
100 + 300 + 131 + 75 = 606
Still leaving 144 slots still open.
I’m not saying the inventory system is perfect (because it isnt) but theres more than enough space to have literally everything that matters.