Enlighten me, o' ye learned ones

I'm invariably a very happy person when I can safely say that I'm ignorant about something. At the same time, I also usually want to know as much as possible, before my failing memory sends me back to status quo.

So here's a few questions about the vote in the Lok Sabha scheduled for the 22nd. As I'm just too lazy to actually dig and find the answers - the Prudent Reader is requested to do so on my behalf and post it here. Surprisingly, the media doesn't seem to be addressing these very much at all.

1. What is a trust vote - any precedent? As I understand it, it is nothing more than a validation of the nuclear deal. As I further understand it, a failure of the UPA to win the vote does not ipso facto compel it to dissolve the LS - the opposition must then initiate a subsequent vote of no-confidence which would then actually topple the Govt. Is this right?

2. Assuming every MP votes, UPA needs 271 votes to win this vote. But lets say that 20 MPs don't turn up at the vote. Does the UPA still need 271 or does it now need 261. (my guess would be 261). Now to further complicate things, lets say every MP is voting, but that there are 20 abstentions. Does the UPA still need 271 or does it need 261? (I don't know, but I'd guess 261).

3. As I'm told by informed sources, the Whip applies and all MPs must vote as directed. I am also told that the 10th Schedule was amended to eliminate the minimum number of MPs required to legally defect and vote legitimately. Lets then say that a total of 20 MPs vote against their Whip. The Speaker, I understand, cannot disqualify them prior to voting. So three questions follow:
(a) if openly defecting MPs are suspended / expelled from their party prior to the 22nd, can they participate or are they obliged to resign?
(b) assuming they vote against thir Whip, are their votes (after they're cast) subject to be disqualified / ordered not to be counted by the Speaker?
(c) if their votes are disqualified, then do they count as equivalent to abstentions or not? In other words, after the 20 MPs' votes are disqualified, is the majority the UPA needs still 271 or 261?

Enlightenment is sought...