Knowing NOTHING about MC, or having your own servers, I want to understand the implications of this Before we go ahead.
Can someone bring me up to speed with the **downsides*** of my son having his own server - apart from costs which I'm told will be in the region of £10 per month.
My son wants to allow only one of his two cousins to play on his new server. Will this be possible? Although his cousins have their own MC accounts, they are brothers and live at the same address so have the same IP address.
Any advice welcome
As already stated there's the advantage that your son would be able to expose himself to working with something he hasn't previously -- managing and maintaining a service provided to others.
That being said, if he's simply going to be running this at home for other people he wants to play with, then I would absolutely recommend hosting it at home. Minecraft in fact has a built-in feature allowing people on the same network to join a single-player world.
Now then, if he wanted to have people from outside of the home network join, it can be a bit more complicated. Depending on whether he is running that single player world, or a full server, the service for that game will be running on a "port". Any incoming connections to your household will need to be told where to go in order to access the game, also known as "port forwarding". It involves going into the router and making a forward for the computer in question. So in that case, it's a lot more viable to do something like that for a desktop computer with a permanent server that won't change very much.