A potion of Lightning Bolt would not be a legal potion. The Feat Brew Potion states which spells can be turned into potions:
You can create a potion of any 3rd-level or lower spell that you know and that targets one or more creatures.
Lightning Bolt doesn't have a Target, only a Range and Area.
If you allow potions of Lightning Bolt anyway, the most likely way that they would work would be to hit the imbiber with a lightning bolt. Whether or not it hits any other targets would be pure DM fiat.
Bonus 1: An unconscious person drinking any potion has teh same effect as a conscious person drinking that potion.
Vampiric Touch is a valid spell to put into a potion, since it targets a creature.
The rules on potions state:
The drinker of a potion is both the effective target and the caster of the effect
It works just as you say; you drink the potion, take damage, gain temporary HP, and then can heal yourself back up to full with the extra temporary HP.
Bonus 2: There isn't anything specific on this that I can find, but it's likely that you can put metamagic feats on potions, as long as the total spell level is less than 3. For example, you could Empower a first level spell, since the total spell level is 3. Quicken definitely wouldn't work, however: you're not casting a spell, you're drinking a potion. The spell's casting time is totally ignored, and replaced with the standard action to drink a potion.
Bonus 3: By RAW, no. It is a standard action to drink a potion, and there's no RAW way to dump a bunch of potions in one tub to drink more quickly. Houserules on this are common, but it basically comes down to what your DM agrees to.