If we're going for realism he'd probably not be saying a whole lot after he got stabbed for the umpteenth time, even if the knife was led by his adoptive son
First stab was delivered, according to Plutarch, by Gaius Servilius Casca while his brother Publius was holding Caesar. Then the rest of conspirators started swarming Caesar and stabbing him. Main sources cite different last words: Suetonius mentions as a hearsay that Caesar said "You too, child?" in Greek. Plutarch wrote that Caesar didn't say anything at this point but covered his face seeing Brutus among murderers, and his last words were "Casca, you villain, what are you doing?", in Latin at Publius holding him so before the first stab.
So the famous "Et tu Brute" is Shakespeare joining both versions.
more like 15-20 i think, but yeah. but they're far more regular and behave more like prepositions do in english.
the worst part of IE cases isnt that there's so many of them (there arent, the most ever is like 8-9 and that's in ancient languages i think), it's that each little case marker means a multitude of things at once. see above how it ending in -i means it's one of multiple possibilities, and each time that lone little -i is marking both case and number together.
so for the above Dative example, hungarian would have (contrived, yes, i know):
Odaadta a lovat a Brutusznak - He/She gave the horse to Brutus.
Odaadta a lovat a Brutuszoknak - He/She gave the horse to the Brutuses.
the -nak signifies the dative (more or less). the -(o)k is the plural. so a plural in dative is -oknak. it's not some third thing, it's just a concatenation of the individual suffixes marking number, case, etc.
Polish languange have half of its grammar rules ripped straight from Latin and surprisingly it works better than in Latin. Horror to learn for foreigners though, or so i heard.
Yes both are indoeuropean languages though the distance to that common ground is far, but the grammar was ripped since Latin was mandatory for the educated class in the entire X-XIX centuries, included especially the period when Polish language was first used widely in writing.