Just to make sure I have it correct, "The Mandalorian" takes place 5 years after the events of ROTJ, right?
If that is the case, then it took Boba Fett approximately 5 years to recover his armor. Did he spend those 5 years with the Tusken tribe? He was wearing the black Tusken robes when we first see a glimpse of him in The Mandalorian. That would explain the emphasis being given to his time with the Tuskens. It wasn't just to recover physically but to offer him a new path to follow. I can accept that, story-wise. At least it isn't an instant character change but gradual, over a 5 year time-frame. But that doesn't excuse his actions in the first episode.
As for which new characters to purchase, if made available, there really isn't a lot that I would be ready to throw $250+ at, at the moment. I personally can't justify picking up every new character being introduced, especially if just briefly shown. My quick list based on just the two new episodes would be the female Tusken and hopefully she comes with the mastif/dog thing. I wouldn't mind a pair of the Gamorreans but as bare-boned as they are, they will be ridiculously expensive, I feel. Those are it. So far.