There are simultaneous calls for not using paper in any form because it causes deforestation, but when it comes to building and making products from wood it is considered environmentally sustainable, as new trees are constantly planted.
I don't think any paper manufacturer is using forestry practices where the forest isn't replanted. All of the major manufacturers accept only sustainable wood. The main problem of paper is that it releases the carbon very soon, unlike lumber or biochar that retain wood for at least a century if not more.
Wooden (but not paper) products are praised because of being bio-degradable, although it means that most of the CO2 captured by the tree to form it's structure gets back into the atmosphere when wood degrades (or is burned), and same goes for paper (please correct me if I'm wrong). Both can store it's carbon for hundreds of years, if prevented from degradation, but in such case bio-biodegradability argument makes less sense.
That's true. For optimal carbon retention, wood should be used to make either biochar or lumber from which houses or furniture are built.
I fully understand dangers of plastic (and other artificial substances) pollution, especially if plastic makes it's way into water, but in the last case, how hard is it to keep plastic waste away from rivers and oceans?
Pretty hard, as we have found.
For example consider a garbage can in a public place. When garbage is thrown there, birds start to search the garbage can for nutrition. They distribute the plastic waste everywhere. Wind moves it to the nearest river, where it goes to oceans.
Also plastic used for clothing leaves massive microplastics in the washing water (well, not if you never wash your clothes but I don't think that's a viable solution). Those aren't filtered away. They go to oceans as well.
Also, given the fact that there are maintained forests that are specifically used to harvest wood, black / grey markets for timber are also huge. Could an end consumer possibly find out what is the source for that material? And is the capacity of these special timber-producing forests cover the needs of the entire planet?
The main problem is that there are other uses of land than forest. If the other use is more profitable, it's possible that forests are cut and used for raising cattle for example. However, if planting a new forest is more profitable, then that will be done.
Besides, it's not easy to claim that the demand for lumber caused deforestation. If the demand of lumber is truly high, it increases the price of lumber, meaning the most profitable use of the land would be to plant a new forest.
The real culprit for deforestation is eating meat and drinking milk. Raising cattle requires massive amounts of land.
In fact, if nobody buys lumber from deforested areas, then the forest will be burned. Deforestation was not prevented, and the carbon dioxide due to burning reached the atmosphere immediately. Therefore, I would argue it's in fact good for sustainability to buy lumber from all areas, including those that were deforested. Otherwise the forest would be burned instead.
The current rate of construction is so high that if we needed for example to replace all concrete with wood then no, there probably won't be enough wood. However, even despite this, we should maximally use wood because it's a carbon sink as opposed to concrete that requires cement (a carbon source). Even if we manage to cut only one third of cement manufacturing emissions, and at the same time store carbon, that's significant.
If you want to maximize the chance that the wood you buy is sustainable, you should buy wood from tree species that don't grow in rainforests, but instead grows in northern areas where the other uses of land are not so profitable and thus practically all land is forest. But that won't stop deforestation of rainforests. If nobody buys wood from rainforests, those rainforests will be deforested not by cutting down the wood, but by burning the forest.
If you want to stop deforestation, you should reduce consumption of meat and milk massively.