So, what are the rules of cricket?

Those final moments left me more confused about the rules of cricket than ever before. In particular, the World Cup rain/bad light rules. Surely, the ICC can do much better, at the very least for the showpiece event of the game they administer.

What is a reserve day? When is it used? More importantly, when can it not be used?

Why was the match reduced to 38 overs in the first case? Wouldn't it be a smarter idea to complete the match over 2 days, allowing maximum opportunity for the maximum overs to be played? If, the ICC is okay with that long a World Cup, they can't mind an extra day for the final.

Could the umpires, technically have asked the teams to come back the next day to complete the remnant of the final? Didn't we have a complete match already, as Sri Lanka had already faced the minimum 20 overs?

If it's technically possible for the match to be completed the next day, why was Jayasuriya so worried about the rain clouds hanging over his head? Why didn't Mahela Jayawardene accept the lights that were offered earlier?

If the match could have been completed when it finally was, then why the hurry or need to reduce those 2 overs off the Lanka innings for that very short rain-break?

Wouldn't it have been more sensible to start off with a 35 over match instead of a 38 overs one, allowing for anticipated small-breaks in the middle - those irritating breaks which matter more than the one at the beginning?