Advice on my business plan?

I installed iBooks Author and am now considering business ideas.

I have never authored a book before. I am an expert Javascripter and have a MacBook Air but am relatively new to Dashcode.

I have used an iPad, all told, about 20 minutes.

IIRC Apple's cut is 50%. Which means if I set my price let's just say at $.99 my cut is $.495. If I average 100 sales a day, that's only $50 profit/day or $18,250/year.

100 sales/day for a year seems naively high. But I want to know the potential upside, so $18,250/year is what I estimate my upper limit to be.

This is assuming I can create a nice book. I was thinking of doing a children's story because my son is 2, and if I owned an iPad I would certainly buy from the iBooks children's category. The iBooks Author controls are familiar looking and since I know programming I have some ideas around e.g. html5 storage.

Forget content for now. How much profit is within reach, at what confidence level? At this point, given what little I know, I would have to say I have about 5% confidence that I could make at least $18,250/year.

I am intentionally not considering the multiplying effects that are possible here. If I were to produce several books, these could potentially each earn the same amount estimated above, and I could create a little iBooks authoring factory in my home. The buzzkill is that I am also multiplying my assumptions.

This is to say nothing of my costs. I have to buy an ISBN, spend time designing and authoring content at the computer, purchase art, probably pay Apple a hidden fee, and (need I mention) the opportunity cost of not working on other ideas.

How are these numbers coming out better for you guys? Where is my early, rough business plan going askew?

"It's all about great idea, less execution." - David Heinemeier Hannson