How to set up the sous vide bath for guineafowl breasts? I have a hard time finding hints on how to sous-vide guineafowl breasts properly. Traditionally in an 140-165°C oven they’re really hard to get right. Some of the few recipes i’ve found place them in a bath of ~65-70°C for some 30-120minutes. This feels a bit short for my taste, as i’m not sure whether the breastmeat will reach the desired temperature at its core in such a short time. So the time-temperature for this cut in sousvide would be one point i’m interested in.

Furthermore, i’ve often heard that poultry especially contracts muscle fibers when “temperature shocked”. So i guess i’d start the bath with cold water and cold meat, to get a slow heat-up.

The last question is for sauces which could go well with it. The meat itself should be way more aromatic than many other poultry meats. Due to this i’m not sure if using the liquid from the sous-vide-bag as a base for sauces (i.e. fruity riesling butter sauce with caramelized onions and some mushroom bits? Maybe others?) is a good idea. On the other hand, if not using the meat-juices there’s pretty little base you can make a sauce of … right?
One of the benefits of sous vide cooking is that you cannot cook food over the temperature set, if you set the temp to 70 degrees it's physically impossible for it to go over that. This means that if you cook it longer than it needs to get up to the desired temperature you won't dry it out. I would think for guineafowl that 120 minutes would be enough. As for temperature shock you'd have to go much higher than 70C to run into that, so I'd start with the water at your desired temperature. 

As for sauces guineafowl is very rich and savory, so something with acidity would help to balance it. I like your sauce idea and think it would work fine. Riesling is a good choice if you get one with a more mineral character than a sweet bomb, although a squeeze of lemon can supplement the acidity if needed.