Is it safe to keep your all crypto currency at a single exchange (bitfinnix)?Or one should choose multiple exchanges.
depending on how long you will hold your coins, if only for the short term does not matter you save it in the exchanger, but if for the long term this is very dangerous, because it could be exposed to the hack or close the sudden then your money will be lost, save your coin in the wallet that you hold its private key
You said long term is dangerous and i think its not all long term dangerous.
The lack of exchange can be replaced by storing in wallet which has higher security since exchange is very risk for longer time holding.