The Europa League schedule is going to be a factor for the Gooners, Wolves and United. I expect all to get through and then you have another small turnaround before the next stage. Spurs and Chelsea will (probably) go out the Champions League so they might get the benefit of rest, even if Mourinho has made Spurs shite (injuries blah blah).
Since everyone hates this long Champions League stage taking place over 6 weeks, I wish UEFA could have made the Champions League kick in in line with the next round of Europa League and let this round of Europa games take place on the Tuesday and Wednesdays that the CL games are. Give the teams a break from the Thurs-Sun schedule and give the Europa League one round to shine without being overshadowed. But money talks I guess.