I'm beginning to dip into the mad world of Sourdough.

[dpibel]

2. I don't claim to be an expert

I've been baking a couple or three loaves of white sourdough bread a week for about three years. I've added various things: fresh-ground wheatberries, brewing malt, oats, and always landed on plain white. But I'm pretty sure your whole wheat will be fine.

As for how much starter, I'd say about as much as you like. I just use half of mine per loaf, so I can feed it at the same time and end up with the same volume.

Just pick an amount and subtract from your recipe the amount by volume of flour and water to equal the flour and water in the starter (half and half, traditionally). This is easy for me, because I do it all by weight. It may require some parsing to figure out the amount of flour and water to subtract from your basic recipe. OTOH, you could probably just add the starter without any adjustment and, at worst, end up with a slightly larger loaf. But if you're using a small amount of starter, you probably won't even notice. And, given the fermenting time in your recipe, I think you'd be fine with just a tiny amount of starter. It's just like store-bought yeast: It reproduces like crazy.

Most sourdough instructions I've read have you discard half your starter, feed the starter, let the starter double in volume, then take half for your bread. I've not seen the point in that. I just take half my starter, plunk it in with the flour, water, and salt, and let it rip. Never had a problem.