Some answers to your questions, based on my experience with wild sourdough starter in San Francisco:
- 70-80F is the ideal temperature range. Below that the yeast incubates very slowly; above it, the starter will tend to ferment alcoholically.
- Do not leave the starter in direct sun. UV light is a powerful sterilizing agent.
- An organic, cold-processed (i.e. stone milled) flour works best, because it will retain the maximum amount of its own wild yeast on it. Cheeseboard: Collective Works likes to start with rye flour and gradually add bread flour, but they don't give a tested reason for this.
- I have never heard of using fruit juice in a sourdough starter. I would be dubious about it; you'd be likely to end up with vinegar.
- Sugar is unnecessary for sourdough starters.
- Use purified water; chlorine/chloramine/ozone in tap water can kill your starter.
Finally, starters incorporating milk are fridge-only starters (as opposed to flour-and-water starters, which can be kept at room temperature if split frequently) which depend on the bacteria and lactic acid from the fermenting milk for part of their sourness. They can be effective, and actually a good choice if you live somewhere with weak/poor wild yeast. Note that you cannot transform a milk sourdough into a water sourdough, and using up 2 cups of milk every 2 weeks is more expensive than 2 cups of filtered water.
Without seeing the loaves or knowing your exact procedures, it's hard to guess. My money would be on too dry a dough. Could also be inactive starter, too long a bake, not a hot enough bake, not enough rise time/temperature. So I'll just talk about how I make sourdough in the hopes it'll help. These are techniques I've learned from various books (most notably Reinhart's The Bread Baker's Apprentice) and experiences.
If I did it right, you can click any of the thumbnails for full size images.
First order of business, of course, is having a nice, active starter. I build my final starter from the barm the day before. Depending on my schedule, I either leave it at room temp all night or feed it earlier in the day and pop it in the fridge. It then comes out to warm up a few hours before I bake. It should show strong signs of life. This starter was made with nothing but flour and water--no grapes, no commercial yeast, no juice.
Then comes mixing and kneading. I like to mix the starter with the water first, allowing the starter to break up and dissolve a bit. This ensures good mixing with the final dough. Then I add the flour and salt, mix to a coarse ball...
...and switch to the dough hook for 5 minutes or so. The dough should be stickier than you think it should be. Turn it out onto a floured surface for 4-5 minutes of final kneading by hand to adjust the flour. It should be smooth and supple, still be a bit tacky, and pass the windowpane test. When you stretch it to form a boule, the outside should be smooth and not tear.
Let it rise 3-4 hours at room temp or slightly warmer (a closed oven with a bowl of hot water works well). Then shape and proof for another 3-4 hours.
I start with a very hot oven. 500-550F for artisan loaves. If using a stone, get it in there 45-60 minutes before baking, that way the stone and oven get a good heat soak. Then when the loaves go in, you want to create steam to allow the bread to rise before the crust hardens. A steam pan is a good idea, and I also spray down the walls of the oven with a squirt bottle. Be careful of squirting the light bulb--it will shatter. Don't ask me how I know. After a few squirts, turn the heat down to your final baking temp. I usually go with 450F.
Don't forget to slash them, too. That helps them expand and prevents blowouts. I had some issues getting these guys onto the stone (not my finest hour), but they were still outstanding. You can see the crumb is open and light, but still gelatinized and chewy. Perfect, in my book.
Best Answer
As a point of reference let's look to this "Sourdough Starter Recipe"
The ratios are a little off and you are just dumping everything in at the start. Despite your stated desire to "not do so" what you would be doing is making a sourdough starter...but what would probably not be 'a very good one'.
Edible is a matter of taste, yours would probably qualify in some 'technical' sense (unlikely that someone would become ill from eating it) and it 'would be sourdough'. The process of gradually adding and removing flour and water through the week stretches out the food supply. Your "dump it all in at once" approach would likely cause the yeast to multiply too fast to the point of creating a toxic environment for the yeast, however I doubt it would reach that level in 5-7 days. Since you aren't trying to create a sustainable culture that would not be your concern.