How do I keep the same IP when starting over from scratch?

There is not a way to reserve a specific IP address on your account so that it can be re-used on another Linode, however if you rebuild your Linode instead of creating a new one, then it's IP address will not change. When a Linode is deleted, you could open a Support ticket to see if we can reclaim it's address to use on your new Linode, but there is never a guarantee that it hasn't already been assigned to another Linode that was created in the interim. That Linode would also have to be in the same datacenter as the original Linode, as the IP address cannot be transferred to another datacenter.

Would be nice if the image you rebuild from was a clone of one of your other nodes.

You can transfer IP's between linodes
Build a new server, switch IP with old one, delete old linode

https://www.linode.com/docs/guides/managing-ip-addresses/

This doesn't work if you're using an IPV6 SLAAC address, which most everyone probably is. Only a /116, if you have it assigned to the data center where your Linode is, will transfer to another Linode. This involves more configuration than the typical IPV6 configuration does. I believe only IPV4 addresses can be transferred in this way.