Can the President use executive orders to establish the strategic reserve? or does it need to go through the legislative process?
Most national reserves are managed by central banks. In the United States, the Fed is the national reserve management agency of the United States and is an independent organization and not subject to the control of the United States government. So Trump or any politician who wants to add bitcoin to the national reserves would need to bring the proposal to Congress for a vote.
It is safe to say that there is no other viable solution than convincing the parliament and needless to say, we all know how time consuming and difficult that will be. To be fair, a bitcoin reserve strategy could still become a reality, but it would take a long time and possibly even decades.
Currently bitcoin has grown rapidly, all because bitcoin symbolizes freedom, sovereignty, and independence from government control. So it is not surprising that a strong country like the United States plans to make bitcoin a reserve asset of the country, if this is successful then indirectly bitcoin will have a little impact on other countries that will also follow in the footsteps of the United States. However, the problem is that making bitcoin a reserve of the country is not easy because as you said there will be many twists and turns that must be gone through and of course it will take a long time because certainly not all American officials agree with this, especially opposition politicians will definitely put up resistance that makes this effort fail.
Moreover, the Fed also emphasized that the US central bank will not explore storing reserve assets in the form of Bitcoin. The FED also dismissed the possibility of storing Bitcoin reserves on the grounds of legal constraints. So here we can see that the Fed is not allowed to own Bitcoin. The Fed Act is also final and they do not want any changes to the law. Even if this is proposed in Congress, the Fed will still fight because it does not want any changes to the law at the Fed.