I've asked my parents if i can have a minecraft server, my mum doesn't care but my dad says i cannot because he believes that if i was to set-up a server then it will open up a port in the firewall, from which spam and spy were can get through. My Question is if this is true?
The server is a complete other thing than the client.
If you host a 24/7 nitrado (or any other gameserver) it won´t run on your PC. It will run at the gameservers website meaning that there is no way you have to open ports.
Your dad is clever, but you can tell him this: If a hacker wants to be on your PC, he will get in it. Even AntiVirus/Firewall etc won´t change this. And Minecraft should already be allowed by your Firewall, otherwise you wouldn´t be allowed to connect to MP servers (i think).
My friend also hosts a gameserver, and there is nothing running on his PC.
If your dad still does not believe, he can ask a Nitrado staff member, read the FAQ or ask an IT guy.
It is completely save and he does not have to worry about scammers, hackers and so on.