Every time I spin up a new instance of ubuntu I am unable to connect to the internet without editing /etc/resolv.config and setting nameservers,

Put the DNS nameservers as specified in below links when creating/updating the private-network.

Creating/updating private network


Unable to ssh/ping to my instance from outside world even though I have floating-ip assigned to it

Edit security-groups and allow ssh/ping to your instance. Unless you do that, you can’t access those ports on your instance from outside.