Any football manager out of work will be spending a lot of time watching games, highlights, and basicallly scouting players and teams wherever and whenever. Appleton would have know his next destination was likely an EFL club and would have been routinely keeping an eye on all games / teams as a result.
The minute the Blackpool vacancy came along he would have built a dossier on each and every player and the club overall as well developed plan and tactics and list of possible transfer targets to suit his plan. It’s all a pretty standard part of the coaches job interviews now.
Theres databases full of scout reports and coaches reports (not dissimilar to Football Manager games) he would have utilised. The club would have provided up to date scout and coaching reports from the staff most recently at the club (a bit like school reports essentially) and he would have spoke in depth with the coaches, analysts, physios etc. He’ll have used every contact he has to build a picture of the players currently at the club but he will need time watching the players on the training ground.
He’ll know pretty quickly where some players are needed (such as lack of depth at RB) and the staff at the club will tell him what the opinions were of Critchley, thus giving him a little nudge in terms of where priorities may lie - but I would imagine he’ll need a few weeks to make his mind up in terms of the players at the club and whether replacements / improvements are needed. He will of course have players in mind he wants in regardless and they’ll likely be players he knows well or has been tracking at previous clubs.
I don’t think the job of fully assessing the squad will be done for months yet, as competitive games are essential, but I do think we’ll see arrivals soon.