A quick comment in relation to the senses thing: I think that our characters already have sensation, but not the specific ones that relate to the "senses" as we know them here on earth. Before those can come to be, I think there needs to be a physical form. Eyes to see, and ears to hear. Our character don't need eyes or ears to comprehend light and sound, but for it to truly be the "senses" I do think those things need to exist. Which means that they can't really be first. They'll come after form already exists.
Right now, Aysus needs a bit of time to adjust. Its whole existence, there had been nothing except itself and Tahaan. Now the whole universe is filled with something. It'll get better at accepting the new as more new comes to exist, but that was a big change. I'll probably have them create a few more points of light, maybe a larger sphere of light, before they embark on anything else. However, once Aysus gets past that point... Silence probably. Before sound. Because there is nothing yet to make sound, And it makes sense that Tahaan would lead the next one. And then Aysus would balance it out with sound. Which would be a small, subtle thing at this point, since the only things that can really make sound are Aysus and Tahaan.
A quick question: How do things that are Sound, like Song, relate? Does making sound allow for everything that relates to sound, like speaking, to exist? Or do those have to be created independently? Or, since it is an idea rather than something specific, do they become, simply by sound being?