So, you have very similar conditions to me … 1500 feet more altitude, but that should not have much affect, in fact I think our range of altitude helps things move along but not too fast like over 5-5500.
Anyway, I hesitated commenting because I do know that for every 2 bakers there are 4 opinions and it can be difficult to sort out what to do, especially when you are learning. I did comment because before I started my own starter, I read all sorts of things about needing to have higher temps. When I finally just gave it a shot … no issues.
A. There is NO problem with changing flour in starter. You can transition your starter to whole wheat, rye, white … whatever you want. A lot of bakers like a rye or rye-whole grain starter. I started with the white and it works well for me. ***
B. You are absolutely correct. It should not (and need not) becomplicated. But even among well known professional bakers, you will get the “it must be this or it must be that way” scenarios … vastly different between bakers. You know what? It is flour, water and salt
My 2 cents here … stick to your feeding plan and see what happens with the whole grain. Then … try the no knead sourdough recipe on this site to start … no fuss. The Breadtopia bread flour and the Sprouts whole wheat should work well and I wouldn’t think there is anything in either flour that is inhibiting things. Water - your procedure should be fine. You can also try leaving the water at room temp the day before you bake. I know people do that with city system tap water to allow inhibiting stuff to evaporate. One concession I make in light of my cool house is that I do warm my bowls with hot water before mixing … hot water, pour it out … bowl is warm and then a cover is keeping some extra humidity in the bowl.
*Edited to add. While you are waiting on your starter, if you do plan to try the no knead sourdough, take some time to watch the video. When you go to bake, pay attention to how the dough feels. You are going for the look and feel per the video which might mean a bit more flour or less. I like to error on the side of less flour starting the mix and then add to the consistency. The no knead recipe is pretty forgiving on this, though, which is why it is a great start.
*** A bit ago, I started a whole wheat and yogurt “stiff” starter for a specific recipe. It was ready in 5 days. I’m not advocating that, just noting that I tried that, it worked well, but I prefer the simplicity of my white 100% hydration starter as well as the results.