Haven't had any experience with Self-Directed Brokerage until now. Is there supposed to be something in the Plan Document stating what % of a participants account they can invest in self-directed brokerage? Also, do many of the institutions (ING, John Hancock. . .) limit the % an individual can put into self-directed brokerage portion of the plan?

The plan document should certainly indicate those that have the authority to direct the investment of plan assets and to what level.