To complete any conversion, with success, always seems to require a good understanding of the existing environment and platform.  In fact, I would not move forward without the background analysis work products. You may want to consider some analysis of what is already in place, and understand:

1. What is the objective of the conversion?  (Always a good critical success factor to keep in mind)
2. Do we convert EVERYTHING?  (Consider your project scope)
3. How different is the converted data?  (A different data type in the new database/platform may require us to CAST data to a new type in the conversion programs.  This can add more complexity to those programs.)
4. Do we have a tremendous amount of data quality issues?

I use the following list as guidelines for an in-depth review of the current environment:

1. All input and output data sources (interfaces) – these can be difficult to find, and you may need to dig deeper and find programs that insert, update or delete data.
2. Reports – any reports coming from the current application will need to be duplicated in the new environment or decommissioned.
3. Spreadsheets – there are probably lots of these around the corporation, analyze as many as you can, and look for similarities.
4. System inventory – I hope you have one of these it should show platform, database, table, and column information.  Consider a bit of profiling for data sampling, as well as look for the data model.
5. Existing ETL jobs/programs - An assessment of the current application could easily take 3 -4 weeks (depending on the complexity).