In this survey discussed the use of u-boot that goes into the composition of the image Armbian, which is recorded on the SD card. When i'm create an Armbian image, the build system automatically adds the u-boot image. This u-boot (from the SD card) is used to start the system only when there is no u-boot loader in the TV box itself or it is corrupted. In all other cases, u-boot is not used on the SD card. There are several variants of u-boot for different platforms (s905 s905x s912). On the SD card when building the image (in the image Armbian) can only include one option. To use other options, you need to write it manually (replace the current one). Now, when i'm create an image, it gets a variant of u-boot for s912. This option can only work on models with s912. Therefore, I want to exclude from the u-boot image. If the user needs (when he has a serious problem with his TV box, when the regular u-boot does not work from the internal memory), he will be able to download the desired option (just for his platform) and write it to the SD card.
In this embodiment, is used a regular u-boot from internal memory. This means your answer to question 2.