If the Shoestring was supposed to have flaps they would have been designed into the airplane. Neither the full scale nor the 1/4? scale airplane have flaps. That should tell you something. The airplane lands just fine without flaps and I can't think of a single reason to add flapperon mixing(that is what you will be doing) to the original plans. The plane lands a little hot and takes some skill in landing, but it isn't unmanageable and is a very popular airplane. Keep the speed up on landing and literally fly it onto the deck and you'll be fine. It isn't a beginner's airplane, more like a third airplane. Also, I think it is out of production.

Regards,
doubledee