Most platforms supports buying and selling through Bitcoin, and most places don't support it, so it depends on where you are,  if your country doesn't support it then you change it to a Fiat before use, but Yes BTC is a long term investment so as such you Hodl.

Most altcoins are risky to invest in, that why I tell anyone that wants to invest in an altcoin to carry out a comprehensive research and bear in mind it is a 50-50 chance for a DIP or a rise in price and values,  some years ago (Early years of BTC) investors didn't really know what was coming, but after the ups and downs of BTC look at where we are today, so the same goes for other altcoins, don't expect a shirt term profit, make a long term investment on this altcoins and Hodl it,  they might not surge in price as Bitcoin, but they will make a significant rise in price, but if the altcoins start experiencing a DIP then take it to be a 50-50 , either a profit or a loss,