Re shopping, honestly this is one of my least favoured parts of the game. Also we were apparently very unlucky with loot since if we put all of the groups funds into just Llewellyn he'll still be behind on WBL and that's ignoring Samuel.
My suggestion would be to hand wave this and bring everyone up to normal WBL for level 10 with the proviso no one item is worth more than 1/3 of WBL and move on.
My personal preference is to just keep going with whatever the adventure hands us and what we can trade. It is more immersive, and I find APs tend to get easy at higher levels if you go full gear up.
As for handing the campaign, we can wait a bit more. We really don't lose much for not having the control of the campaign, while moving to another thread is a big blow to the sense of continuity.