Flashing both FW and EMMC cleans the device pretty thoroughly. To do back-to-back flashing, you need to do clean flash and then immediately flash the open mode kernel, so that the device does not boot between the flashings. Android needs no partitioning, it can run from your Harmattan partition. To boot sailfish you need to repartition, but it can be done (and actually should be done)) after flashing ubiboot kernel.