I understand the nervousness about how many changes we're making at the back and a lot will depend on two factors:
1. Pre-season
2. The extent to which the players just "drop-in"
On pre season firstly, there's always a risk that when you make loads of changes that players don't gel together straight away. That means they need loads of time working together on the training ground, and also in pre-season games. The normal situation with the latter in recent years has been more about giving opportunities to fringe players. Pre-season games often have totally different XIs in each half. That bugs me, and we've often got to the first game of the season without anyone playing a full 90 in pre-season. In some respects, the Community Shield will help on that score. But it takes exceptional coaching to bring a new defensive unit together and to create the necessary chemistry and understanding without lots of game time together, and realistically the players aren't going to get that. I wouldn't be surprised to see Frimpong and / or Kerkez phased in rather than going straight into the starting XI.
On the "drop-in" factor, I'm thinking here about some of our recent defensive signings who spent quite a bit of time on the sidelines before securing a first-team place. Robbo didn't go straight in, nor did Fabinho (a defensive player, if not in defence) and Kostas was obviously cover. The likes of Bradley and Quansah would have been learning the system for ages before they made their debuts. By contrast, Virgil went straight in and, injuries aside, has been there ever since because he was a perfect fit, the archetype player for his position - the system was built to bring out the best in him, even when he wasn't here. So it's quite normal, Virgil aside, for players to be eased in and I expect a bit of rotation here as a bare minimum with the full-backs. If Ibou goes, I wouldn't be surprised to see Gomez start, injury permitting, ahead of Guehi / AN Other at the start of the season, if only because he knows the drill. But as others have said, it's also why there might be a preference to keep rather than replace Ibou, even if it's only for 12 months and I would rather see him help us win more trophies than flog him for a knock-down fee this window (because it would be a knock-down price).
But here's the thing. If I can work that out, I reckon Arne can too, and he'll either be careful with his initial selections or coach the shit out of the players in pre-season so some or all of the new guys can go straight in. I also reckon he'll not be banking on making huge changes to how those guys play, and he'll have tactics in mind that they can adapt to easily enough and which play to their strengths.
