Using an Ultra as a phone replacement

Long time samsung watch user here. In an effort to cut my screen time I just upgraded to a watch with a Sim, so I can leave my phone at home when out and about. After carefully reviewing stats (especially battery life) I went with the pixel 4, but I have buyers remorse. I just can't get used to the interface, and I'm missing my watch 5.

Thinking​ the Ultra might be my best bet if I want to switch back to Samsung. I am still within my return window so should be OK to do so. I have a couple of questions though:

-with a paired watch line (so the # is the same as my phone) is my phone required to be on in order to send texts? It is with pixel watch which is really annoying as it will lose connection after a few hours and not be able to text any more.

-realistically what can I expect for battery life with mostly wifi usage but the occasional few hours on LTE? No Spotify or anything but occasional maps usage. I'm getting about 1.5 days from the pixel 4 which is disappointing.

-how is Bixby? I never used it in all my years of samsung watch use but with leaving my phone home I need to be able to tell my waych commands like "text Mrs. Smith will be with you at 10am", etc. Does it work well for that sort of thing?