Trying not to overanalyze, but wondering

No, I don't think that you're being unreasonable. I would be worried too. But it does depend on a couple of things - first, how long ago did they break up? If its a matter of weeks then yeah, I'd be sweating about it because his emotions and feelings for her will still be pretty current.

Second, who broke up with who? If she broke it off with him then he didn't just stop loving her and he'll still have strong feelings for her.

Third, what's this about "he doesn't anticipate that he'll hook up with her or that she'll stay"? If I had a new b/f tell say that, I'd quietly and politely explain to him that if he wanted to hook up with her or have her stay over at his place that would be fine. That would show that he clearly wasn't over her and clearly wasn't into me - so do not call me on Monday.

I would want something a little more promising and assertive from a new b/f. There is certainly no reason for her to stay. If she stayed over that would be it as far as I was concerned.

And there is no good reason (as far as you're concerned) for him to go through their stuff with her all day. It's either hers or its something he doesn't care about or its something that he wants. And usually stuff he wants would boil down to a handful of things that can be covered in a phonecall to the ex. Its not something that he needs to spend all day with her "organising to give away or sell". Frankly I think he's using that as an excuse to put you on the backburner and see what happens with his ex. He's just as likely to call Monday and say, "Hey lollipoplollipop. You're great but me and the g/f have decided to give it another go".

Edited to add:
Should you call him? I'd say "No". This is one time when you want him to sort himself out and know that he was thinking of you enough to call you.