Are you trying to harden your box for a reason? A lot of linux boxes have special apps to help you. What OS and version of it do you have?
uname -a will show that, so please post it.
No but you can't be too careful. And sometimes my laptop is connected to free WiFi.
I 've got two laptops: ubuntu and debian
1)Linux 4.4.0-57-generic #78-Ubuntu SMP Fri Dec 9 23:46:51 UTC 2016 i686 i686 i686 GNU/Linux
2)Linux 3.16.0-4-amd64 #1 SMP Debian 3.16.36-1+deb8u2 (2016-10-19) x86_64 GNU/LINUX
My point is: you can break all kinds of services without knowing why. And if someone attacks a random port and there is no service behind it to respond, the attacks fails. So no need to block it. This is why attacks go for a lot of known ports. So known ports may require a minor tweak.
You mean I'do better to change default ports rather than block them?