After spending all of my 35 consulting years in the defined contribution practice of Towers Watson, working with very large companies, I know 401(k) plans. I know where the problems occur, how to fix non-compliant issues, the government requirements and especially the compliant interactions with the non-qualified plans.
Just to get things started....here are the qualified plan limits, estimated through 2022. Also included is the denominator (the Base CPI Number) that the government uses to develop the new rates so you can do your own estimates. More 401(k) highlights to be added soon.