Quick opinion on first off camera setup..

Hi, Sounds like a good starting plan to me.

Re long ETTL cords: the coiled ones are OK if short - but I guess you will want something longer, in which case I would advise the non-coiled variety. They are lighter and very much less likely to pull over a light-stand.

At one time Cowboystudio did a nice metal Umbrella adaptor with brass spigots top & bottom which also had the hole for the umbrella shaft not at 90 degrees but at c 10 degrees off the perpendicular - making it much easier to centre the Speedlite beam towards the centre of the umbrella.

Good luck & have fun!