I would like to see us get the defence sorted out before we did anything else (not this window I would add). It seems critical to Ange's system.
Our defenders not only need excellent all round defensive abilities, they need pace, ball carrying and passing skills. The full backs need to be technically good enough to create chances and in Udogie's case (or his replacement) as an auxiliary forward.
What we've seen is that the system doesn't really function when one of Romero, VdV and Udogie haven't been available. That's why we need cover for every position.