Hi Max,
(not an expert, but to provide you with some feedback).
You could also do a lot with SPARQL and regular expressions, although that is another learning experience. Your second question would be suitable for this I assume.
Finally, we are looking into ShapeExpressions, but that does not really help to check whether the values of your item confirm a predetermined structure.
So what I am trying to say, there are lots of possibilities to validate the data within your instance. Clearly define what you want to check provides better way to find which solution might fit your need.
Does this help?
Best,
Maarten