I still don't get the buying part of the game, which is probably my biggest failure with it. Where can you buy something like a Tabula Rasa? I've only ever seen magic items at best when I've bothered looking at the purchase items of the NPCs.
I did however use some handy items from some on the latest character as bases for improving them because they had the right sockets already for what I wanted and were improvements on what I already had.
Most certainly, second and onwards characters always help, with stashed cast offs and/or saved currency. Even stashed gems are useful if you haven't leveled them up :)
From other players with currency orbs like chaos orbs. We use a site called http://poe.trade/ to find and contact players that are selling items we want. Then you message them and if they too want to do the trade they invite you to their hideout where you trade.
Ah, right. I have heard of that, but never used it. I wish they had a decent internal method for trading