Beethoven wrote this:
So a piano version should at least be this:
Yes, the orchestra sustains, the piano has a percussive attack then an immediate decrease in sound. You COULD do this:
Probably not necessary. Our ears accept the convention that piano notes sustain, even though in strict acoustic terms every note is a sfz dim. The The sustain pedal will add richness to the held notes too.
How long to hold the fermata? Up to you. Are the first two phrases separate, monumental declarations? Or are they the opening statements of an impassioned speech, ever pushing ahead? Different orchestra conductors have different ideas. Your feeling is valid too. Just don't fall into the trap of thinking 'This is SO well-known, I must do something quirky with it'.