If you have a lot of data sitting in your Adabas files, this migration may take a long time. Also, you may encounter significant performance issues if your table design is to be the same as Adabas - so consider how you might handle archiving older transactional data at least as well as breaking up very large records into multiple related tables.
Beyond that, I would recommend asking SAG for professional services to aid in your attempts as they have helped other customers in such migration projects, as well as for a cost-benefit comparison with moving to Adabas/Natural on Open Systems in comparison to the target you mention. Other vendors exist also who specialize in such efforts.
The biggest pitfalls are 1) how to reproduce all the business logic in a completely different language, 2) how to migrate the very large data files to another DBMS, and 3) how to ensure it performs as well in the new environment. Other problems exist such as how to convert JCL to batch files or other scripts, what to replace mainframe 3rd party products with in the new platform, how to ensure the reliability and availability of the new platform and so on.
Stepping back, if your Adabas DB is very large as most seem to be, and this is a mission critical system, as most seem to be, rather than trying to rebuild it in another language on another platform, perhaps it would be better to buy a commercially available product that performs the same functionality, and engage professional services to help with the migration. Many cases in the buy vs build case, it is much more desirable to buy in terms of both cost and success rate.