You don't lose anything when your membership expires, you just aren't allowed to use any of the members-only content on free worlds.
Yes, this.
Also, holy crap, how do you guys get that much stuff?
Hoarding. I obsessively keep items from quests, and items that I use frequently.
I just got rid of about 60 something items, and made nearly quarter of a million doing so.
Also it's pretty easy to come by money while being membership, I personally can get a million an hour but keeping a hold of it is another thing.
There is bossing if you're lucky and strong enough, slayer if you have the attention span, just various of methods.
If you have good starting money, flipping items is good too.