diagnosed last week with ALS.... He has a tracheotomy and feeding tube.
The previous responses are right on: pulmonary secretions are often managed for comfort with proper suctioning, a cough assist machine, medication, and pulsating vest therapy.
However, most people with ALS have established relationships with ALS specialists of various disciplines before they get a tracheotomy. Just one week after a diagnosis, I imagine your family need a crash course on more than just the questions you asked, (which already have been answered appropriately).
If you have not already done so, you should immediately contact your local chapter of the ALS Association and tell them your situation. Hopefully they can help you line up appointments with the ALS-literate doctors and therapists at an ALSA-certified clinic.
Also, if your father has a life expectancy of "a few months," he may be eligible for hospice care, which can be a real blessing if you can find a hospice that has the experience and resources required for an ALS patient with a tracheostomy. Some people may tell you a tracheostomy disqualifies and ALS patient for hospice, which is not accurate. If the trach is required for comfort care (such as managing copious secretions), that is appropriate for a hospice. The hospice should also supply the cough assist, medication, pulsating vest, and everything else required for the patient's comfort, for free. Please see my previous post about the care that a hospice should provide:
https://www.alsforums.com/forum/general-discussion-about-als-mnd/37355-myths-about-hospice-care.html.
As for knowing when the end will come, predictions are notoriously speculative. We were once told by two ALS specialists that my wife would be dead in a matter of a few days, but she bounced back smiling and survived another year. In her case, the final ending was preceded by increasing periods of sleepiness, which is a very common scenario, but as Diane said, it can also happen very suddenly, which we have seen happen several times in our local support group. In the meantime, providing comfort is the key, and just being there is a big part of that.