You know, a simple "Thank you!" is enough. There is no need to be overly enthusiastic about any person, especially not in a user support forum.

I'm glad that my suggestions helped to solve the problem.

With respect to further knowledge about the Fleur code I suggest you have a look at the different sections in our user guide available at: https://www.flapw.de/

If that doesn't go far enough there are also references to original publications provided. A general introduction to the FLAPW method is also available in the book by D. J. Singh and L. Nordström: "Planewaves, Pseudopotentials, and the LAPW Method".