u r lucky - may and october are delight to sail in Croatia (me from there and sailed a lot). The prices for bareboat charter are unfortunately incredibly higher than in Greece or Turkey, but that''s croatian mentality. This below is the best charter company I know, good boats and FREE mooring in every ACI Marina, of which they are around 20 in Adriatic. That''s cool in May, you will need a hot shower for sure.
I don''t work for them, just sailed with them many times. As for the itinerary, pick any island south of Sibenik (Vis, Hvar, Lastovo, Mljet, Korcula, and Elafites: Sipan, Lopud, Kolocep). This southern route is always better weather, better sailing and better small family-run restaurants on far away islands. If u choose for this kind of route, let me know, I can give u some phone numbers where to eat...I REPEAT I DONT WORK FOR ANYONE. enjoy life
svebor (from Croatia, obviously:-)