Hi woelki, just to point out you have until April 30 2019, to complete your MCSA Office 365, this is when the 70-346 and 70-347 exams are retired, which was extended by one month. 

 

Your choices for further certifications are dependent on what you want to do next, check this post for lots of details [Start with Our New Workload Certifications to Become a Microsoft 365 Enterprise Administrator] it includes the following:

 

Microsoft 365 Certified: Teamwork Administrator Associate

Microsoft 365 Certified: Messaging Administrator Associate

Microsoft 365 Certified: Security Administrator Associate

Microsoft 365 Certified: Fundamentals

 

I put more details in this article, in case it helps -  Microsoft 365 Training and Certification. To be clear though there is no upgrade or transition exam from the MCSA: Office 365 to one of these new certifications.  That's not to say there won't be any overlap with some of the new exams and knowledge you have acquired already as part of your studies.  

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