Anyone know the if the most up-to-date Rhythm package can be used in Dynamo 1.3.4? or what is the most up-to-date version that will please? thanks!

The latest version works.

If there was something more specific you wanted to ask or expand upon, feel free to add it. But Rhythm is built as ZeroTouch on purpose. This allows for backward compatibility for most nodes. There may be a node here and there that uses newer Revit API calls, but for the most part you should be good.