Richard, you picked what is in my experience two of the most challenging cuts of meat to cook competently. Employing several cooking techniques compounds your challenges. Since you have previously cooked brisket, rely on your experience.
With the details you provide we can give you some accurate SV cooking information, thank you.
When repackaging, match pieces of meat with about the same thickness in a bag. And yes, align them together, don’t stack because that doubles their thickness and adds considerably to their cooking time. I learned to cook using larger pieces and whole briskets and i still find i get better results with them than small cuts with too many surfaces that become dry in secondary cooks.
As for that flat, you cook it separately or with the points unless you want distinctively different products of your cook. I’d cook them at a low temperature but for at least a day to tenderize it, about 140F suits me. The higher the temperature you cook at the greater the amount of moisture the meat gives up as it becomes more tender over time, up to about 3 days. Pull the flat at half time because it’s significantly thinner than the others and it’s likely getting more moist cooking.
Your 2-part question:
Part A. You need to think about how SV cooking transfers heat to meat over the cooking time. Please think about this, it’s important you understand the following:
Given sufficient cooking time based on meat thickness the internal temperature of any item will be at or very close to the water bath temperature. It can’t be higher as there no other source of heat than the water being heated by your Anova at its set point. Meat temperature can’t be lower as there will be temperature equilibrium throughout the cooking vessel as long as Anova is functioning at its set point.
Please read it again.
The terminal internal temperature of anything you cook will be at the temperature you selected. Never higher, nor lower.
Part B. You want to know how long to post-cook in an oven or on the grill, most likely the oven.
That would be better. as you have greater control.
Saying, “some crust” isn’t helpful, but i’ll leave how much up to your experience and good judgement. I feel like asking how much damage you intend to inflict on your cooked meat, but i won’t. Do you have a convection oven? If so use it at 275F for a couple of hours after applying your rub. Take a quick peek after an hour, and then every half hour, to judge how the some crust is developing. The longer you post-cook the crustier your result.
Bonus question: about . . “liquid ingredients seasonings, etc. help fat from being dry?” The fat won’t melt much in SV cooking so it cannot become dry. In the oven it will crisp as the bark forms. As the seasoning rub darkens in the oven it absorbs more heat which drys it ever quicker.
Remember those peeks? You be the judge, but please don’t over do it.
Cooking is always a matter of balancing competing outcomes and you are the judge when you’re cooking for yourself.