thank you very much for the elaborate explanation. Most of this I already did...and failed. Basically turned the sonoff into a (temporary) brick. As its (most likely, need to test this first) turns out I used the wrong flash method (QIO) while on the tasmota github site it cleary stated that the DOUT method is the only one that works. Its late now, but im gonna retry that tomorrow, if that works then another step has been taken. I still would like to get tasmota working, but thats for a later stage.
once more: thank you
o and great site! (superhouse).