Heyo! So from what I am getting you want to change your ip from 127.0.0.1 and change it to like something like: play.myserver.net right? Well it's actually pretty simple, head over to https://www.noip.com/ and register an account, everything is pretty straight forward from there. Also its free! But you will get ip's ending in .zapto or something like that, if you want ones that end in .com or .net you will need to pay and it's actually really cheap. Also if you are using the free plan don't forget to renew the ip every 30 days. Hope this helped !
Not all the time, if you are using a vps its not needed. If you are using the pocketmine pc software then yes