Is there any max inventory and management in the wastes?

I don't think so. I have dweller returning at the moment with over 70 items. He has been out exploring for nearly 4 days.

The longer a dweller is exploring, the better the loot that they find. Increasing the level of the dweller increases the amount of hp that dweller has, meaning they can stay in the wastelands longer.

As Erhardt de Kock said, in 1.3 it seems that the carrying capacity of dwellers has been drastically lowered. I'm sending out people who have max stats and they keep coming back with next to nothing without giving them a chance to explore. As far as I know, sending out more dwellers does not affect how much one dweller can carry. Strength affects what types of monsters they'll attempt to fight (and possibly kill, not sure), while Perception and Luck can increase item drops. That's about all I know.

Some are saying 100 items, that seems right. Just today got a message from an Explorer just over Three Days out, "Well that's as much as I can carry, better report back to the Overseer." He automatically started coming back, and the Explore Button is Greyed out. I counted 104 items, but it's probably 100.

I dont know if its still relevant. But my dweller returned automatically to the vault after collecting 104 items. Still 11 stimpacks left en 24 rads en couldnt carry anymore items.

Exploring was just over 3 days. This dweller had 8 strenght, 8 endurance and 11 luck. Had and -49% damage reduction pet.