Yeah, that wing-fuse crossing makes for a nasty diffusor. The fillets may be necessary due to lower aspect ratio than the Zlin trainers have, so bigger AOAs. Might have to do with spinning as well (blanketing).

The Z-50 has symmetrical, good-natured NACA 0018 tapered to 0012, good for a strong wing. Together with the 0.8 planform taper the airfoil taper makes for a total 0.5 taper ratio - good for snaps. Obviously, the 1 degree dihedral is sufficient for the low wing position. Did you notice that both wing and stab have a decent positive incidence angle?

You mean the Z-50 M with the Czech inline engine (called Minor) and the bigger rudder. As far as i know, the stab is the same as on the L (Lycoming) versions. I wonder why you had trouble with the stab, but maybe it was due to the struts. The original is said to have a weak spot where the tail meets the fuse, kind of a structural bottleneck.

Unfortunately, I never flew one, only Z-142, so my knowledge is second-hand.