1. 0.1? You must be high as a kite. Since 1981, the rate of increase per decade was 0.32. But before the decade is out it will probably be about 0.60. Then in less half that time the average will be around 1.8. Then in less than half that time, it will be around 2.6. That is if we're lucky and it only doubles. But being exponential in nature, we could be talking about a 5 degree increase in just 2 years. Then a 10 degree increase in just one year. Then a 20 degree increase in 6 months. Or maybe a 100 degree increase. It's hard to say. But the hotter things get, the faster they will get even hotter. And unfortunately, there is plenty of methane in areas of tundra and in frozen methane hydrate ice on the sea floor.
2. Protected in whatever way they need to be. Both from a fire without or a fire from within.
3. You just don't have any air or moisture in the sodium tank. If there is a void needed in it at all, you could use something like argon gas.
4. You make my point. A further point would be who knows how many miles of piping. Some of which would have to be perfect in construction.
5. From ground level, I would say a man made lake about about 5 foot deep and 5 acres in area would do the trick.
Also, seeing how much you love my graphs, I have another one for you.
View attachment 767026
This picture of methane rising from the sea floor might also interest you.
View attachment 767027