Glad to see someone "from the other side" engaging in honest discourse. I'll start out with saying I do not have all the answers but the general situation is that even as a collective we do not have the exact answers the cost of inaction is estimated to be VASTLY larger than the cost of action. (A ounce of prevention is worth a pound of cure)
1a) I am unaware of any studies about the optimum planetary temperature. But there are several other points which would likely entierly negate any benafitfrom "re calibrating"
1aa)Massive calibration costs. Society has spent many hundreds of years with the climate relatively stable. The costs of adjusting to a slightly different (even slightly more optimal) situation. New Orleans is a prime example, as stupid as it may have been to build a city with much of its land subject to such major fluds, moving the whole city now is not exactly a cheap prospect. Multiply this by millions to to get an estimate of how much it would cost to adapt to significant sea level changes.
1ab) Who's to say the the optimum is not lower?
1ac) The best counter point is that the best science aviliable suggests that it will not be a "modest change" It will be a fright train and we have no idea where it will stop.
1b) There are two main ideas for reducing global warming. Cap and trade, and a carbon fee. There are ways to combine these and other methods to best optimize for the "unknown" exact amount. Any way most in the environmentalist camp... I guess I would consider myself in it situation....would be happy with the LOWEST POSSIBLE ESTIMATE. The estimates are so very high and dire that even adapting to the lowest possible estimate (while having some valid research behind it) would be a massive step and a place most would be happy to start with
1c) Yes people will die. If we find 1b) and apply it, a free marketer would estimate the correct number of people would die.
1d) This is more a political issue. But if you were to take bare minimum reasonable actions, it is reasonable to assume that everyone who "puts in" by "cutting emissions" would get more back via cost savings to make it worth while for everyone.
2) The cost of taxing or capping and trading on the oil production itself would be low ish if we it directly at the resource production level. The costs would be spread out into the industry as a whole as economics dictate. The overhead of taxation really is not that huge. And from the estimates I have seen for the cost per KG of carbon (in environmental damage) would far far outweigh the overhead.
3) Yes a global agreement could be a problem. But..... As much as we talk about global warming as a GLOBAL problem. It is also a local problem. The effects of these emissions are much more intense in the immediate area.
Economists have studied this rather intensively. Just to give a taste if you are in the relative vicinity of a major carbon source. Your walls need to be painted more often, your car breaks down quicker and you are less healthy. Economists have put a lot of effort into modeling this and they do have values for this.
If you account for these local costs, each individual nation should already be taking MASSIVE steps to curb pollution.
In short the details you want, while theoretically important, only would become relevant in a much more ideal situation. If we took the bare minimum steps to meet and deal with the bare minimum estimates from economists and climate change experts the effect of the details would by stunningly minor in comparison to what has already been achieved.