i2b2 allows labels that are supposed to be shown to the end users to have a length of 2000 characters. This would be equivalent to nearly one page of text and is of course unsuitable for the limited space on a standard computer screen.
It's better to limit the designation of a concept or folder to 40 characters at maximum, most can be even shorter. But be precise: it's better to label a concept "Date of admission to the ICU" rather then "ICU admission" or "admission date" because every concept should be understandable on its own.
In the i2b2 navigation tree, folders are displayed before leafs. It can be disruptive when clinical forms contain some data elements with codelists (folders on level A) and code list items (leafs on level A+1) while other data elements have continuous values (leafs on level A). In this case, it is advisable to