Yes Wolfman, you've mentioned it!

Serbia is separated from Croatia for more then ten years now, but for long time those countries were connected (as well some others) so the languages are extremly similar. Croatians, Bosnians, Serbians, they all use "da" for yes and often "ciao" for good-bye. It is also noticable that southern and western parts of Croatia use amazingly lot of Italian words (ponistra, manistra, lavandin, sentada, la porta, puntizel), some of western parts, like Istra, still speak in Italian, and northern and eastern parts use German and Hungarian words. Serbia and Bosnia difference a bit becouse mostly one language inteferes (per instance Turkism in Bosnia). Also, Serbians talk very similar but they write on Cirilica.

Terry you wrote: Do you know of a book (in English) about the history of the Adriatic region in pre-Roman times?

No, I'm not familiar with that book. But I found a lot of informations in "Povijest Dalmacije" ("The History Of Dalmatia") by Grga Novak - last Croatian pre-historian.
Also Minoans waren't really mentioned.
As I said, they culture flourished while there was culture on this areas. Or they were kept away, or there was some kind of agreement, but as you said:
"Presumably they traded up into the Po valley and so to Western Europe. Perhaps their trade with the Aegean region was via the Danube and Black Sea?" Not sure. There was a lot of tradeing paths, archeological findings confirm that. But most of the history is just guessing.
you wrote: "I read recently that the Illyrian language was related to the East Italian languages, which makes sense."
Illyrians were bunch of nations called that becouse of their similarities. Languages also developed along the way by "adopting" words from other languages. Presuming that they were tradeing with Italy, that is logical. As Wolfman wrote: "Right in the path between Italy and Turkey, between Moscow and Rome." Being in the middle explains the diversity inside the language.
We still notice those words - we use them every day.

Oh, and yes. Mostly all surnames end with -ic (pronounced as itch smile )
Croatian, Bosnian, Serbian, practically every surname from ex Yugoslavia, so you'll find Jovovic, Andrijasevic, Juric, Mitrovic, Papic, Vladislavic, Jelovic, Kostelic, Cosic,...
Only some surnames from Lika seeme to differ (like Zobenica or Tesla) and those derived from other countries (mostly Italy).