As with all journeys, the length of the journey and the challenge of the terrain to be traversed depends on where you start.
The advantage and disadvantage of IBM i is that applications are compatible with earlier versions. It is possible for a program that was written on the System/38 in 1980 to run (with no recompilation) on one of today's IBM Power Systems. The benefit is that, as hardware was replaced and improved, applications did not need to be upgraded or changed. Unfortunately, the same applications are written using code and coding techniques that might have been leading edge twenty plus years ago but fall short of today's requirements.
You need to determine the following items: