Please follow this guide how to set a static IP for your node
http://community.umbrel.com/t/how-to-set-a-static-ip-for-your-umbrel-machine/
Not really, just for setup the IP is not necessary.
Anyways, mSD card can be reflashed anytime, there’s nothing to worry about doing that. Is just the OS on it, no user data, LN data. All user data is on the SSD drive.