From what I understand, a balanced D&D party needs for archtypes: A melee fighter for dealing with other melee fighters, a rogue for detecting and removing traps and locks, a caster for dealing with enemy casters, and a healer to keep everyone standing.
A party limit of four really completely kills gameplay diversity in my mind. Are there any good multiclasses you can do with a level limit of 10 that can let a character handle two of those roles without crippling themselves at one of them?