Hi,
Your approach seems fine
You have a for loop in a for loop because foreach is like a loop. Only consider that foreach does not garantie the sequence (depending how the interface is written). So you code seems fine !
As for OOP you have to think an object as a black box. An object has inputs (properties, methods), and outputs (events, properties). An well written object does not now about objects it does not belong to or way around. Whit that in mind you are thinking OOP