I am not sure if using lowercase for :PROPERTIES: and :END: is a good idea – it seems that Org assumes they are uppercase by the looks of the function. It may just work fine, but some internal search / regexp code may be case-sensitive and potentially behave unexpectedly.
An alternative idea may be hiding or prettifying these syntactic elements. As an example, see this post of mine and the thread around it.
This is just a suggestion. Lowercasing might just work fine. But if your intent is purely for aesthetics, then the suggestion above might save some troubles long term.
Edit. In the post I linked, I said “Use lower case for properties meta data” – I no longer do it and I have simplified my setup. Today I use org-modern to simplify the UI and my setup for Org mode.