I've seen different times and temps so I have been trying to hammer that out as the party is this Sunday. I am thinking of going your route. Smoke to 185 then water bath at 150 for 24 hours. If I need longer I will just drop it down to 140 and let it chill till we are ready to eat. Think that will be good?
Never tried it, but I'm in the camp of smoke it like a day before the way you normally would and then let it cool completely in the fridge (garage fridge for me) until the next day.
You could then SV heat it up and then slice it hot at the party.
No matter what, you want to smoke this brisket long enough so it comes out tasting like bbq brisket and not beef pot roast. If you smoke uncovered to 185F that should do the trick.
Also I'm a big proponent of smoking it whole and not separated. This is because the Flat muscle is the problem child and benefits (in my experience) from having the point muscle still attached. You place the probe(s) in the thickest yet center-most portion of the flat muscle to let the thermometer tell you when to start checking for tenderness all over (around 200F for me to start checking). It's not easy to nail the sweet spot so I use 2-3 probes from slightly different angles and go by the lowest one because it's the one that is the likely closest to the sweet spot since it's a lower temp.
Finally, I also am a big proponent of trimming a brisket where you cut off the thin end of the Flat muscle so that what is left of the flat is about uniform thickness with the thick portion and you can repurpose that good thin flat meat for grind, stews, braises, etc. Here is what I mean:
Trimming like that usually means you don't want to separate flat and point since you cut off like 20% of the brisket as it was.
Anyhow, just some food for thought. The main thing is to land on something you know will work for sure that you will be comfortable with. So this is why I'm in the camp of smoke it early the normal way and reheat via SV or oven or any other means the day off. Smoked BBQ always tastes better the next day anyhow and if you nailed your brisket to begin with, it will still be perfect and juicy when reheated (but not overheated).