Also, wouldn't this mean you have to pay interest on the ENTIRE amount of the loan, as opposed to tax on just the gains? So if you have $1000 that means at 2% interest (I assume that's yearly) you're paying $20/year, whereas if your stock went up 5% (= $50), that means you'd be paying (say) 25% of that, which is $12.50. So it should be only better if either have a high tax rate or your stocks /really/ increased in value (not just kept pace with inflation).

That requires 110k$ and you can't just take money with that rate, it's margin. So you should have more than 110k$ to take some of that money and replace them with margin.

What happens if your stock goes to zero in the meantime while you've borrowed against it?

Broker will sell your stocks to prevent it's losses.