Hello! I am very greatful that you have asked this as these are great questions.
1 - The Red Weed system will most likely be fully remade and will be much faster and more realistic and actually grow instead of just appearing out of nowhere near the Cylinders.
2 - They will probably be added in the next major update, [0.5 era], when I am planning to remake the whole map.
3 - The buildings have a normal state where it's just one mesh of the whole building and this is the one that is enabled at the start by default, there is then a script that checks for when the Tripod Foot hits anything with a certain tag. Once it does, the buildings normal state is disabled and then it enables the destructable state which has multiple different parts and meshes in it and then they are all destroyable when a Tripods Foot collides with them.
4 - Yes.. it will be improved, optimized, and may use a whole new system near release.
5 - The current buildings are 100% prototype and they will be fully replaced at some point.