that's it. Thanks to whoever answers.

Objects placed in containers have a tendency of getting "eaten" by the game. If you place too many objects in a cell, a Overflow Loot Bag will appear, containing all your stuff.

Other than that, no time limit. NPCs aren't going to pick up the Daedric Dai-katana you left on the docks of Ebonheart.

Yup, no time limit. Unlike in Skyrim, things you place do not get reset/respawned.

The exceptions are Guild supply chests, and a couple of merchant crates, etc. Those are set to respawn, so use them at your own risk. Due to the "ownership" of containers affecting anything that is placed into them, it's probably safer to just drop your items on the ground, up to the cell limit allowed before a "loot bag" is generated (varies with platform, but around 1000 items on some consoles, FAR higher on PC). Bandit caves, with "not legally ownded" containers, are also safe storage.

you can leave your stuff anywhere and it will remain indefinitely. I always use spare rooms in some of the bigger mages guild halls and lay weapons, armor and books out on the floor or bed, put soul gems and small baubles on tables and use the chests for potions and ingredients.

no one will ever take them, move them or toss em in the trash. if you do use "owned" chests make sure that you close doors or are hidden from view as anything you take back out, even though it was yours, can make people hostile.

I never knew about the 'loot bag'. I'm on PC and I suppose I've never left that much stuff laying around, even though I'm a bit of a collector for sure.

On PC, the Loot Bag shows up after you place 1,024 items into a single cell. Keep in mind that items in containers don't count towards this, so you could have around 1,000 items just laying around all throughout a house or something, and an additional 500 items in chests/closest/etc., without getting the Loot Bag.