Well I think to start, and we can always come back to this list, let's do something that's a little more developed and ready? That way we can get a feel for each other with something that's ready for us. Since I play Natasha most often I'd say she'd be a good place to jump off from. Post avengers is a good place to go because pre-avengers I most often see Natasha bothering Tony as Ms Rushman. [ which is my hc of why she wasn't in NM with Clint. - she was finishing up stuff with Fury and Stark while he was sniping Demi-gods ] 

The good thing about Natasha is that she brings a lot of baggage to the table. So to top off all the mess with whatever gets Steve out of his little hermit hole to be the good guy again, there can be all sorts of trouble following the Spy too. Which means we can start off simple, just some trouble makers coming around to rough up a quiet town... and go from there - someone with a vendeta coming to cause trouble for the spy. We'll be able to get plenty of time for them to get to know each other a bit, work together, and get some challenge beyond regular punks coming to stir the pot.