Prelja you are totaly right about Ljubljana. The thing most foreginers dont know is that Slovenians didnt call (and most still dont) Ljubljana realy Ljubljana but Lublana. Most Slovenes and especialy older people say Lublana not Ljubljana. We use Ljubljana becouse of 19th century illyrian movement which wanted to create south slavic language.
About Veneti i dont know exactly, but it depends on which Veneti you think. There were many people who were called Veneti example you have Adriatic Veneti then you have Veneti in modern France and then you have baltic Veneti. Maybe there connection but it is open to debate.
Usualy early west Slavs were called Venedi in latin sources. South germans called Slovenes and Serbo-croatians Windisch. North germans called Sorbs, Czech, Slovaks and Poles Wenden. Maybe there is conection.
Here is on flag showing Venedi: