Can the President use executive orders to establish the strategic reserve? or does it need to go through the legislative process?
the president cannot unilaterally issue a policy on the national reserve-- the bill would need to go through legislative debate and that would involve the fed, and other relevant agencies. that's why trump's plan to create a national reserve with bitcoin is not a near-term possibility because it would require further debate by lawmakers and many other parties, until it is approved by a majority of lawmakers and then the bill could be implemented.
on top of that it seems trump also want to consider US coin first, so really right now it's pretty much unclear about national bitcoin reserve, it could be national crypto reserve made up of bitcoin + other US based coin for all I know in the future, we definitely only be speculating here because at the end of the day, we don't have any clue at all about this other than probing the crystal ball.