Hello there, as you have a lot of points to touch on, I'm just going to get straight to how I can help you with your project.
First things first, if you take a look at my portfolio, you can see an example of an eBook I've ghost written. You will notice I use proper grammar and formatting. The example book was on a subject I had absolutely ZERO knowledge of and yet you can see that I was able to research it and give quality information.
That being said, when it comes to computers I have 19 years of experience and consider myself to be an expert. I am who family and friends call on when they need help with anything relating to their computers, tablets, mobile phones, etc. from the basics all the way up to the advanced. In addition, I am currently a student working on a Bachelor of Science in Information Technology degree. In other words, I know the subject matter well, and then some.
I can write well in any tone you like. I will make your reader feel they are learning from a friendly yet knowledgable source, that they can learn the basics of computers with no problem, and I can do it all without being overly technical or making them feel like they are in over their head.
I am a native English speaker, as you have requested. You have stated that you want a 200-250 page work. My bid is for 250 pages. If it were to end up being less than 250 pages, I of course would come down on the price.
Thank you for taking the time to read my proposal and I look forward to hearing from you soon.