I would fast until it’s somewhat comfortable, only water (maybe tea if warm liquid is totally needed, it is for me).
But we are all different. I wouldn’t even think about salt in the first 3 days under normal circumstances but if I felt dizziness, I would eat some. But many people needs it on the first day.
3 days sounds very nice to me but only if it’s comfortable enough. Determination tends to help.
Of course, it matters how much energy we can get from our fat reserves… I had plenty of extra fat on my first, longest EF, I got hungry after 5 days but I was obsessed with food towards the end (without real desire to eat. part of me wanted food, probably while the rest didn’t). But it was fun and I satiated my curiosity.
I would eat very well (but not too late) before to make the first day ridiculously easy but this is individual too I guess.