Columns on Steam Profile are limited?

Not sure what you mean with columns, do you mean showcases or something different?

Yes, 10 in total on 100 level.

I was wrong, people write possible put every available showcase once. If you have empty slots.

Seems to be 1 showcase every 10 levels. I'm lvl 43 and have 4 showcases.

Yes they have a limited amount of characters, so at some point it just cuts off if you put in too much.

In custom info box, there's a limit of 8000 characters.
Is that what you mean?