Are platelets, proteins, and vitamin K all required for homeostasis?
I think you meant hemostasis not homeostasis. The former is the physiological process of bleeding arrest while the latter simply means a state of nearly constant condition that our body maintains.
Now assuming we are talking about stopping a bleeding , let me first review some basic principles. Remember that whenever there is a damage to our vessel wall, our body responds with three mechanisms :
Vasoconstriction to limit the blood flow to that region
A primary platelet plug formation to stop bleeding from that damaged area (primary hemostasis). But the plug is weak
Formation of a meshwork of fiber like substance (fibrin) on top of the platelet plug to stabilize the weak plug
Now with these concepts in my mind let us figure out the answer to your question.
Firstly, the roles of platelet is obvious because it forms the platelet plug (it actually takes part in all steps of hemostasis)
By proteins I assume you meant the clotting factors. The fibrin, I mentioned before, remains in blood as globular protein fibrinogen. In order to form polymerised fibrin from it, a series of reactions take place, reffered to as the Coagulation Cascade. Many clotting factor proteins participate in the cascade, acting as catalysts.
Vitamin K is necessary for the formation of some clotting factors (specifically factor 2, 7, 9 and 10) in liver.
So the whole process of stoppage of bleeding (hemostasis) requires all three of them.