Reus seems to be the most realistic world class player we've been linked with, and I still don't think Dortmund would let him go.
Ki is a very decent bench option, if Im not mistaken he can play CB too but we have decent back ups at CB already. We might need to get a 3rd starting caliber CB so that Bonucci/Romagnoli can get the rest they deserve, and also the 3 of them can challenge each other all season
Conti fully fit is probably top 2 RB in the league. Granted Calabria is killing it currently. With that being said you can't just suddenly bench Calabria as Conti will need a lot of time for one to get match fit and two to build team chemistry. I think both Conti and Calabria are capable of putting in a good cross with their left foot, so they might both be able to play on the left. Calabria already played on the left under Gattuso and he was average, so maybe trying Conti on the left might be the smarter option, which would also give him the opportunity to attack the goal more often