I used to teach a class at the community college that covered much of what I
think you are looking for. We used two different books.
One book was called "Mastering the AS/400" by Jerry Fottral. I think it was
later updated by Jim Buck and renamed "Mastering IBM I". I have not seen the
revised book. It does look like Jim Buck added some chapters about
modernization or at least modern tools. Published and sold by MC Press (also
available at AMAZON) MC-store.com shows the current edition available as a
.PDF. The hard copy currently is on sale for $26 saving off of the regular
price. The PDF is on sale also.
The second book, which I am having trouble recalling the name or the author,
I liked it a little better. It was either privately published or a very
small publishing company. I know the school the author taught with was in
Florida and believe it was a community college. I am thinking it may have
been Jacksonville State Community College, but that may not be correct. If
that was the school, I don't think he is teaching there still. It may no
longer be available.
Both books covered things like:
System organization (libraries, objects, files, members, etc)
SDA (screen design aid)
DDS for file creation
Physical files vs Logical files
RLU (report layout utility)
If memory serves, the second book also covered some limited modernization.
You may also want to take a look at this web page: