I've also managed to configure a Galaxy Watch 4 by following the tips in this thread (installed the 3 Google apps in sandbox mode and allowed nearby devices).
I'm currently running gms sandboxed but in the owner profile to get all the notifications such as phone, SMS, IM, etc to work. I haven't sign in with Samsung or google accounts, yet, I don't feel that comfortable with this config. What is your opinion regarding this? Did you manage to get the same but with a work profile? What kind of data am I providing to the big players besides the one described in GrapheneOS docs?