No 2 people will be the same. 'Lots' is my number. TBH, I stopped counting 90s. I don't collect by number but potential usage.
After many years, I've still only 5 mousselines, 5 cashmere including 100s and CSGMs, 3 Maxi-twillies, 3 (normal) twillies, under 10 45 & 55s, and under 10 70s. Proportionally, to my 90s, the other formats are insignificant because I wear a 90 almost daily.
By order of priority, I'd say think about:
1. Format
It will relate to your style and the purpose of what you wear a scarf.E.g. If you only ever wear a scarf for warmth, outerwear and total undone, glamorous casualness, you are better off having 10 x CSGM and no others. If you are a gamine and just want an Audrey bow to signify H, you're better off with a few choice twillies and nothing else.
2.
a) Design
A scarf is personal. Never buy a design that doesn't chime with your personality.
b) Colour(s)
Buy scarves where most colours work throughout the scarf so you don't constantly have to hide 'bits'. If you only look good in pink or blue, luckily for you you can stop after a few choice scarves. If you suit quite a few colours with the wardrobe to match, you may keep finding gaps.
3. Scale/style of pattern.
Again, this may determine that you could be happy with fewer if the scale that suits you is more extreme, or look much better in strong geometrics.