perhaps there was a legal limit how much foreign currency you could buy, but as long as you had a proof of origin of your local currency you were fine. buying 10-15000 dollars or german marks was definately allowed, and nobody would need more in one go anyhow.
i remember as a kid my parents had both dinar(local) savings accounts and foreign curency savings accounts in banks. i don't know when exactly this became legal, but in 80's it was widely practiced. thinking about it, it must have been legal in the early 70's as well, remember the lada 2101 story...
yes it was common to import second hand goods from other countries. some small stuff was allowed to go tru the customs without dues, but TV's, VCRs, cars, fur coats etc were very expensive to import, often 200% duty. often those were actually new goods, but as soon as they were out of the box they were oficcially "used". if you came to a border in a car returning from "the west" with a TV, VCR, stereo and a fur coat, you would be charged customs duty. if you had 3 VCRs, they would simply explain to you that importing more than one in one go was considered commercial import and you should start export import company. that lead to funny situations since it was allowed to cross a border as many times as you wanted, so you would literaly leave your companion on one side while you took VCR to other side, paid customs duty, than returned for the next and so on... as long as customs officers stamped your passport you were fine. of course, if they noticed you were crossing the border often and importing stuff, they would inform tax revenue service. this naturally led to smuggling. customs officers were notorious for taking bribes to look the other way.
there were always "shortages" of something in yugoslavia, or some items were unresonably expensive.
one year it was cofee, so everybody brought it from greece comiing back from vacation.
next year leather jackets would come in fashion so everybody would go to turkey to get few lot cheaper than locally
then price of gold jewelry in romania would go down so people were crossing borders wit half a kilo of gold chains around their necks
those who lived near the borders would cross over even for weekly supplies. detergents, butter, whatever...
technically and legally, you were allowed to bring in what was on your person without customs duty, so you could ocassionally see someone on the border in august wearing a fur coat waiting in line to cross