Agreed fieldgate. It is much more demanding and dangerous than bare rocks, but still enormously rewarding. First time I did it was more than two decades ago, and like Karonny, a million things were going through my mind. But as I said earlier, doable and immensely rewarding. Few tips for Karonny;
a) Biafo is a good choice
Dangers:
1. Unpredictable weather, Scorching hot one minute and freak blizzard next. So be prepared.
2. Crevaces: Deadly indeed and many. However, local guides know the safe routes.
3. No medical support after Askole. Unless you have pre-arranged heli-evac, you are on your own. Biggest threats i foresee is a broken bone, may be twisted ankle. More than that will be bad tummy. Bloody thing just saps all the energy out of you. So stock up on flagyl and antibiotics before hitting the trail.
B) Fitness, both physical and mental. You will be hiking 8-10 hours a day. On top of that high altitude and walking on ice take a heavy toll body and mind. Best way to counter that, take it easy, don't rush. Give yorself at least two weeks. You may finish a few days early. No harm done.
Best is to acclimitize yourself and do some light, high altitude treks. Skardu- deosai- skardu would be good.
C) How many porters? Difficult to answer. It all depends on multiple factors. When i did it the max. weight limit/ porter was 25 kg. But that was long time ago. May be other forum members can give current limit. Its no harm hiring a a couple extra and lighten individual loads. They are not very expensive.
Hope this helps.