How much do you-as-DM tend to give, either overall or relative to guidelines? Flip side: how much do you-as-player like to get?
I've been using the 5e generation tables lately - maybe eyeballing it if it turns out too low, high, or repetitive. I've got the tables set up in a spreadsheet so it's just an F9 to recalculate. As a player, I'm flexible about how much I like to get - depends on the edition. 5e, it's not that big a deal compared to 3e/4e.
How much of your treasure is magic items vs non-magic?
Mostly non-magic cash and art. Magic items are a bit rarer in 5e in general, which suits me fine.
How do you "place" it in adventures? By this I mean is it sitting there easy to find, is it hidden, is it always guarded, is your expectation that the PCs will find all of it or miss some, etc.
If it's useable, it's being used. Otherwise, it depends on the lair and the creature. Some are secretive and hide things, others just lock it away, some sit on it.
How does your group divide treasure and who decides the method used? Also, how often (if ever) does your group divide treasure?
We divide cash up into n+1 shares so that there's always a party fund for group purchases, components for raise dead, etc. A lot of healing gear ends up there, at least temporarily, as well. Otherwise, we typically divide loot up according to a who wants it/can use it/has been falling behind basis. We generally don't care that much about value in the short term - we're a
team, we're not going to cash out a staff of power in the hands of our wizard just because everybody else ended up with something much cheaper and lower powered. That would be madness - giving up group power for individual greed?
Who owns the treasure before division? After division?
Before division, treasure is essentially the group's. Afterwards, it's individual - though we have a high degree of cooperation and hand-me-downs happen a lot as upgrades occur. We are a
team, after all. I'd rather boost my teammate's effectiveness than get the cash in most cases.
How easy is it in your game for treasure and-or PC-carried possessions to be destroyed, stolen, or lost? Are your players cool with possession loss and if not, why not?
It doesn't come up all that often really. It can be frustrating to be on the end of that sort of thing, but it's 5e so it's not horrible to lose stuff. I lost a number of items back in 2e days (including a vorpal blade), that hurt a bit but I got over it.
Can magic items be bought, sold, or traded; and if not, why not?
Yes, we generally use the downtime rules in Xanathar's for it. It typically takes a week of footwork and spreading some cash around to find or sell items. Though because of a shortened time between completing one chapter and the next, I did allow PCs to shop for items of common/uncommon value - they were in the Free City of Greyhawk, so it's not like there isn't an abundance of magic around and lots of population to support a greater availability of magic items. Most of them got their first +1 weapons that way (they're 9th level).