I know about this stuff from my work.
i) Dry wood is (approximately) (CH2O)n.
The relative masses are C12H2x1O16.
Perfectly dry wood is therefore approximately 12 parts carbon/30 parts total, by mass. The usual 10-30% water would lower the relative carbon content.
So 1 kg of perfectly dry wood x 12/30= about 0.4 kg carbon.
The units are important, whether it is expressed as mass of carbon, or mass of carbon dioxide, since, for perfect combustion:
(CH2O)n + O2n -> CO2n + H2On
The relative masses for CO2 are C12O2x16; 12 parts carbon/44 parts total, by mass.
So a gram of carbon is not a gram of CO2, and the emissions units are expressed both ways.
Gasoline is close to (CH2)n, and the gasoline combustion would be approximately:
(CH2)n + 1.5O2n -> CO2 + H2O
Gasoline would be (about) 12 parts carbon/16 parts total mass.
ii) Forests can sequester significant amounts of carbon, and not all the carbon that is fixed is re-released through decomposition. During the decomposition process some compounds (like lignin) are highly resistant to breakdown and their derivatives can accumulate in soils as humic acid and related compounds. These compounds are very stable in soil and can persist for thousands of years, sequestered away from the environment. But the accumulation rates per year depend upon (CO2 uptake/year - respiratory release of CO2/year). These rates vary widely with climate with vegetation type and with forest age.
As others wrote, as a general pattern younger forests have higher uptake rates per hectare (or per acre); the re-release rates depend upon climate and vegetation.
iii) As others wrote, wood heat is not carbon neutral, but it is closer to carbon neutral than fossil fuel burning, particularly for domestic heat. The tradeoff with nuclear is complicated, since the reactors represent enormous embedded energy & carbon equivalents.
The bigger problem is that there is not enough wood production per year in North America to meet anywhere near our current energy expenditures. So wood heat is viable for the fraction of households in high-forest regions. Around my area, the current wood supply is partly 'mined', since it is hardwood being cut faster than the regeneration rate, to make way for land clearing or softwood plantations. Carcinogenic particulate emissions are also a problem, since so many burners are sloppy.
iv) In theory, carbon taxes could be nearly equivalent to cap and trade; in practice the accounting for a carbon tax is simple and straightforward, with limited opportunities for market distortion or corruption. Cap and Trade, by contrast, is complicated, with good opportunities for distortion by lobbyists, or for outright corruption. Who sets the cap? Who arranges the Trade?
So, of course, our governments are inclining towards Cap and Trade.
We currently tax labour highly, which discourages labour, wages and savings. We keep tax on materials and energy low. So many of our practices and designs work to limit labour by using materials and energy. We would be better off if the tax burden was shifted OFF income (to encourage labour, craftsmanship, wages, & savings) and towards energy (to encourage energy efficient practices, energy independence, and, possibly, even, limit climate change).
