1. The first half of the question is unclear. If the question is, "can I integrate iPPE and BOM structures for the same finished product, for example use iPPE product structure with BOM routing or vice versa", then the answer is no.
As stated above, it is possible to use production version with iPPE product structure and iPPE process structure assigned to it.
2. Yes, you should create iPPE in ECC and transfer in APO, as stated above. It is technically possible to create some iPPE elements directly in APO, but there will be several restrictions, because not all ECC-related abilities to maintain such elements are supported in APO. You can also check that EA-iPPE component versions are radically different for ECC and APO.
3. The question is unclear. Configurable materials can be used in iPPE as products without material variants, but I suspect that the meaning of the question is different.
4. No, BOM phantom assembly cannot be directly assigned to iPPE product structure.
5. The question is unclear. It is unclear why use iPPE with "dummy component variant". For the same product, you either use BOM explosion in ERP or iPPE explosion (RPM or PP/DS) in APO. Started from some Enhancement Package version, it is technically possible to maintain both BOM and iPPE structures in parallel in ECC for the same product by activating a business function, but there may be additional restrictions.
6. If you're going to plan product in APO, then it is not possible to assign BOM structure for this product directly to iPPE structure. If you're going to plan product in ECC, then there is some obscure approach to use iPPE product structure and "dummy" BOM routing (it is briefly mentioned in PLM170 course), but details are unknown for me.
7. Line Design should exist in ECC (maintained manually or maybe tranferred from a separate SAP PLM system) and transferred to APO via CIF.
8. Yes, it is possible to plan only finished product in iPPE/APO (also via MMP), and semi-finished products (components) may be planned in ECC. There is no need to create iPPE structures for semi-finished products (components) in this case. For this, you should transfer dependent requirements for semi-finished products (components) from APO to ERP, and there is a transaction for it in case of RPM explosion (I don't know about the case with PP/DS explosion). But you cannot use APO-ERP-APO planning chain for products, and usage of APO reports and functions will be very limited for semi-finished products (components). Of course, in this case you cannot use MMP to plan components on the lines in APO (such as cabins, engines, ...).
9. As far as I know, no, this is not possible.
10. It is unclear why detailed routing should be created in ECC for iPPE product. As stated above, it is not possible to assign detailed routing to iPPE product structure via SAP standard ways.