Awesome, thanks for your answers they really help.So in terms of general roster advice, is it best to hold back on transitioning to 4* land until you have several characters ready to go?
You have several fivestars, so I don't Think it would necessarily be a problem to level fourstars as they come. When they are not boosted, they won't be much higher than a fivestar or a boosted threestar so their effect on matchmaking should be neglible. When they are boosted they might affect things a bit, but you probably want to play them then anyway.
Moreover, both Peggy and Cyclops are quite good fourstars and could be very helpful. If you have the ISO I see no problem with leveling them up a bit.