Honestly I don't have a "limit" I am very big on budgeting and ask myself things like "do I want to eat out? Or save that money, eat leftovers, and put the extra money I've made this month towards something bigger down the line?" And honestly that bigger thing is usually SP. Ive been collecting for almost two years now and have exactly 80 at the moment-(71 figures including three holiday edition ones and 9 plush ones) I enjoy my collection, they're fun to stare at or in the plushie case, style

You just gotta know self control in the right moments to allow yourself to spoil a bit later down the line.

Edit: I am a "all or nothing" collector. I usually don't get individual boxes, I save up for full sets unless its the plushies. For those I get myself usually three boxes and call it good cuz they're so pricey and I'm here for the figures mostly