Is there any max inventory and management in the wastes?

Dwellers will find items every hour in the wastes, plus some time fixed events such as: Broadcast Tower, National Guard, etc.

However, their inventory do have a limit of 100 items. After picking 100 items, they won't pickup anymore, although they show up in the log that they have found something.

SPECIALS do affect the chance of finding items and caps. And their level will increase their HP.

Currently as of update 1.03 1.1, there's no way to sell or ignore items while exploring

Please refer to the community spread sheet: Fallout Shelter Efficiency Sheet.

SOURCE: REDDIT

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.