If u dont want to get more stash space, u can just make another account and use it for extra space, GGG allows u to open two clients at the same time so u can move stuff between accounts, its not against the rules.
I only trade a little, its not really needed to be filthy rich, unless u only want to make them expensive builds and rolling in new leagues always is more fun than staying in the perma leagues, plus its actually easyer to trade there since everyone starts from scratch and ppl dont only look for the top tier gear.
poe.trade is a good index site to figure things out about what stuff usually goes for between players, its also pretty sweet when looking for great deals when u need something to max out your resists etc.