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I was hoping Barcelona to meet Benfica, then Paris vs Liverpool.

Maybe that will happen this season and Barcelona's mission to qualify for the quarter-finals might make more sense. But I also don't think Barcelona's chances of getting to the quarter-finals will be low if they meet PSG in the round of 16, of course because we know the quality of the two teams' play this season.
In another side, Arsenal vs Feyenoord, Intermilan vs PSV, Bayern Munich vs Madrid, and lastly, Leverkusen vs Atletico Madrid.
I think that's gonna be interesting fixtures. It seems to me Arsenal will have no chance to get into the semi final following they are in the difficult line.

Any team that has qualified for the round of 16 basically has a chance to get to the next round and the final. Each of them has a different probability, but we might can guess who it is if the drawing results are already available.
Some big matches can be expected in the round of 16, but I don't expect two teams from the same league to meet in this round. There should be adjustments so that two teams from the same league don't meet in the knockout stages, but that's a possibility too. I think a match between two teams from two different leagues is more interesting than from the same league.