Re: do I need a firewall?
You do NOT need an intrusion detection system. An IDS is only useful if you are opening ports in your firewall, which you are not doing.
It's like wearing a knife-proof jacket when standing behind a wall that nobody can get over.
Also, I see from your other thread that you turned on UFW with your router firewall on, and now are having problems with your home network (as I said would happen in my post). Removing the GUFW package will not turn off the firewall. Reinstall GUFW and turn off the firewall. GUFW is merely a way of talking to the firewall built into the Linux kernel. Ripping off a man's clothes will not kill him.
I try to treat the cause, not the symptom. I avoid the terminal in instructions, unless it's easier or necessary. My instructions will work within the Ubuntu system, instead of breaking or subverting it. Those are the three guarantees to the helpee.