Sure, we usually use level blueprint for doing testing/prototype. So you gonna move that code to the BP_Tower or it UI itself.
To get your specific actors, you can use tag.
From your viewport, select a static mesh, detail panel, add tag:
Then from your bp, use the search node Get All actors of that tag name you just set:
Then just use a a for each to add your actors tag to your variable array.
There other solution/method which will be optimised for searching actors (especially if you have a huge amount) so it a consideration to be made for performance.