You’ll find that different exchanges cater to different markets. Today, most countries have at least one cryptocurrency exchange specializing in their own currency. There are exchanges that can accept New Zealand Dollars in exchange for bitcoin, for example. Other exchanges are known for certain pairs. Bithumb, for example, has particularly strong liquidity in the ETH/KRW (South Korean Won) pair at the moment (and it’s easily the most popular cryptocurrency exchange in Korea).
There's a lot of ins and outs which can get confusing in arbitrage trading. We won't go into the technicals of why futures contracts trade at a premium to spot price. You can read a full explanation here. If it's not of interest to you, all you need to know is that there's a tendency, the further out in time the futures contract expires, for the premium to spot to be higher and higher in nominal percentage terms.