I think most on here would agree that at times last season that our defence wasn't the best. That was in the National League, so with them all being one year older and now in a higher division it follows that we need some level of upgrade. All other areas of the team have been improved.
We now have a squad of 19 players plus goalkeepers and under 21s, so that means we could have 3 more.
With 7 subs allowed next season (will the subs' benches be big enough?) I assume he will have a goalkeeper and 6 others - meaning 16 outfield players each match. If we stick at the 19 that would only leave 3 as backups in case of injuries, suspensions or loss of form.