I see no definite borders for EU expansion other than cultural.
There are some problems with Ukraine, there might be if there's too much corruption and oligarchy type stuff, so I don't want to absorb them immediately-- they need huge reforms, but I don't find them objectionable per se. I think they need to get smarter, get rid of their mafia etc., but it might be possible.
It's critical for the EU to prevent this kind of expansionist warfare on its borders.
Unlike you, I don't think the EU had any business participating in this war.
I wouldn't dismiss a nuclear exchange quite easily.