expand_less Multiclassing is allowed and encouraged, following most of the same rules as non-gestalt games.  However, after your first three primary classes, any additional classes begin their CP cost progression as though you were taking your third level in that class.
For example, if you chose to multiclass into sorcerer after already taking at least one level in three other classes, then you'd have to pay 4 CP for your first sorcerer level, 8 CP for your second, 12 for your third, etc.  This means that you'll only ever pay 1 or 2 CP for the first two levels in up to three classes (your primary classes).