Just as with the BiPAP, would advise to start low on pressure and work your way up. Pause time and cycles should allow for recovery and avoid breathlessness. Oscillations are an individual thing that you can try and see what the response is -- too much for some.
RTs tend to "prescribe" a set regimen but they are not trained to recognize the metabolic aspects of ALS and reduced lung capacity/use of accessory muscles that could make this difficult or counterproductive.
Oatmilk and cashew milks are examples of dairy alternatives that are increasingly available in puddings, ice cream, yogurt, milk, creamer, etc. But many PALS can and do fine with traditional dairy, so I wouldn't cut it out unless there's a reason -- there is usually more protein there than in the alternatives.
For some people, citrus and/or spices are triggers for mucus, so you can track that.
For prevention of buildup, warm liquids and/or papaya or pineapple juice, or papaya tablets, help some people, in part because they contain bromelain.
A whole food (less processed) diet with good fats and as you say plenty of high-quality protein could include easy-to-digest foods like pureed meats, eggs, applesauce, canned fruit/veg, dairy or dairy alternatives, avocado, etc., while avoiding raw seeds/kernels/skins.