I can't directly answer any of your points, but Peter H. Wilson's The Thirty Years War: Europe’s Tragedy touches on the devastation brought by the war and some of the causes for it.

The devastation of the war came in two general forms - direct damage to populations caused by pillage and looting, and the spread of disease that followed armies coming from all over the continent.

Looting and pillage are fairly obvious, and the pattern of depopulation we see as a result of the war tells to just how devastating these things were to local populations. Besieged cities were sacked when they fell -Magdeburg, for example, suffered at the hands of Imperial forces and was reduced from a population of 25,000 to merely 5,000. The destruction there was so complete that it didn't really recover to its prewar size for over 100 years. Less immediately obvious were smaller scale assaults on populations. The sectarian nature of the war meant religious minority communities became targets, and armies moving through a "heretic" area would be liable to commit atrocities. But even without the sectarian nature of the violence, the movement of forces was often devastating to communities even in neutral or friendly territory.

The cause for that boils down to the means of supply for armies at the time. As the war moved on, forces in the field increasingly relied on the local area to provide for them as they marched. Soldiers would descend on villages, requisitioning supplies, and, while it was common to offer receipts or IOUs in the likely event that soldiers didn't have the money on hand to pay for what they took, it's perhaps not unsurprising that this often amounted to little more than the army looting the countryside it moved through. Requisitions took no heed to the needs of the local population or the sustainability of their actions, and thus those locals who weren't harmed resisting requisitions were often left starving as the army passed. Even those communities that could weather the army the first time it rolls through would face a heavy toll as armies moved back and forth through the course of the war. This phenomena can be seen on maps showing the depopulation caused by the war - the areas hardest hit were the swathe of Germany on the southwest-northeast axis from Brandenberg to the Palatinate, following the pattern of campaigning for much of the war.

The other, equally damaging cause of this depopulation was disease. War until modern times has been synonymous with disease, and the 30 Years War was no exception. Armies are magnets for disease and spread it to communities as they move. The 30 Years War, having brought men from all over Europe to converge on Germany, also would bring diseases from other regions into Germany. Most notably, the War of Mantuan Succession fought in parallel to the war in Germany would be a source for a plague that swept through Germany after the war ended and Imperial troops were brought back north to fend off the Swedish invasion.