Welcome to this site but sorry for the reason that brings you here.
PSA is not a reliable indicator for PCa, particularly when figures are only slightly above those considered typical for the age of the man. (There are a number of reasons for an elevated figure which among others may be attributable to an enlarged prostate or a urinary infection). However, as the PSA figure rises, particularly into three figures, it is increasingly likely that the man has PCa. This accords with what the doctor said is the situation with your Dad unfortunately.
The HT tablets/injections are a sort of holding or restraining treatment and may be supplemented at some point with whatever the doctors feel is appropriate after they have completed his diagnosis and individual plan.
We have quite a number of men who are at various stages of their individual cancer journeys, some having been diagnosed 10+ years ago. New treatments help extend lives but it is difficult for doctors to forecast how any individual will fare over the long term because men respond to their cancer and treatment differently.
It is the score of 280 combined with the nodule that could be felt that makes the doctors confident that your dad has prostate cancer. The MRI scan tells them whether there is any spread to soft organs such as lymph nodes and whether the cancer is still contained within the gland - a bone scan will also be requested if they want to check his bones.
Usually there is a biopsy but occasionally they don't bother if all the other tests are conclusive. Putting dad on hormones immediately was the wise thing to do; the hormones starve the cancer by knocking out his testosterone. Once the results are all in, they will be able to advise on whether any other treatment such as radiotherapy or chemo will be added.
"Life can only be understood backwards; but it must be lived forwards." Soren Kierkegaard