Yes—this type of setup should work together. A YN560-IV speedlite can be mounted in an S-type bracket, and a Godox umbrella octa designed for S-type/Bowens-style use should fit that bracket correctly.

A 2.6m stand is likely adequate for this combination, especially as a starting setup. The main caution is not so much basic compatibility, but robustness: budget S-type brackets generally do the job, but they’re not built for heavy abuse or constant rough transport.

For portability, this is a practical starter kit, but a 120cm modifier is fairly large for event use and can feel less convenient to carry and set up quickly. Also keep in mind that larger softboxes put more leverage on the bracket and stand than a bare speedlite.

If you continue using off-camera lighting, you may eventually want a boom arm or heavier-duty support to position the light over subjects more easily. But for getting started, your proposed setup is compatible and should be workable if handled with reasonable care.