MacOS Catalina

https://discussions.apple.com/docs/DOC-250001761

Covers the answers to most of your questions. 64 bit programs need to replace any left over 32 bit programs before you upgrade to Catalina. Only upgrade when you are certain you need Catalina to run something.

An easy way to determine which of your current apps will have to be upgraded to 32 bit version is to run the free GO64 app. It very easy to use and quickly shows you which are 32 bit and which are 64 bit.