I'd get the latest Megane RS, that thing is a beast. The brera is nice but unless you get the 3.2L (and even if you do), it is quite underpowered and not the most reliable of the 3. Don't you want to have more options ?
That's a good analysis. Probably no one would buy an actual "ultimate driving machine". To me it seems like the E82 135i is the closest you can get to this. But then for the price of a used one you can get an E46 M3 with low mileage...
Until you leave the dealer, no.
Seriously, from what I read, the ones from the 50s and 60s were very prone to rust and until the 80s they are known to have big realiability issues. But if you are a bit mechanically inclined and feel like starting an Alfa project, they will bring you a lot of joy.