I think it's Teach next . I've no doubt anymore he was looking to get an AW ( Pluton ) , that's why he brought his whole crew to go with him .
In comparison , he just send Burgess alone to get Mera Mera no mi , a pretty powerful Logia ( infact was able to clash with his Yami & i think Sabo is gonna be an Admiral with it ) .
So yes there is no doubt he was looking to get something more powerful than Mera , and i think an Ancient Weapon is the only option that makes sense . I doubt Oda was directing him to Mihawk as he's not evil & is Shanks' friend . Plus Mihawk was already Marines' target .
After getting Pluton , he's gonna be so confident that he'll go straight after Shanks , and again - he's already brought his whole crew with him too . By the end of this year their battle will start , and will set up Teach as Luffy's next opponent in Road Star or Raftel .
As for the Admirals , i think 3 of them ( Akainu-Kizaru-Ryokugyu ) will be defeated in the Final Arc .