Upgrade from 4.0b to 4.6c

[Robin Sahasranam]

We are just staring our project to upgrade from 4.0b to 4.6c. We have over 20
custom workflows in production. The workflows and tasks are of all types (WS,
WF, TS, T). We use only a couple of SAP delivered workflows.  Our workflows are
in area of approval/release of purchase requisition, purchase order, service
entry, trip, asset disposal, AP invoice payment and a few custom applications.
 
Some of the workflows are copies of SAP workflow with changes to role resolution
function and work item text. We have not implemented SAP HR or loaded the org
chart, so all role resolutions use custom functions which go against custom
tables. We also have several custom Business objects to support custom
applications and enhancements to SAP Bus. Object, to add custom attributes and
methods.
 
I am looking for some guidance and information on how to assess the impact of
the changes, estimate and plan the upgrade. Initially, I want to gather as much
relevant info as possible.  I have access to the Release Notes for 4.6c and the
intermediate releases as well.
 
Are there are other free useful sources of information? I am especially looking
for useful tips, do's, don'ts etc.
Are there any particular OSS Notes which provide useful info?
Any other information you are willing to share from your upgrade experience?
 
I am extremely grateful for any assistance you can provide.
 
Robin Sahasranam
World Bank