Its so much better than backing up to ZIP files on floppy disks. 8)
Usually, I’d use mock data and set up Firestore once I’ve achieved the desired level of functionality.
I used to create a Git repo as a first step, but stopped doing this because 1) I’m not worried about a hard drive failure during the initial development, 2) I want to get straight into making progress on the core idea, 3) I currently do all development on one laptop.
Or I just scramble to get something that works just for me, to make sure it makes sense, even if it clearly won't work for others w/o tons of modification.
Edit: Before starting to code, I register a domain. It’s not a great habit because I’m now paying renewals on domains I don’t use. It builds up over the years.