If I were you - I might switch all the free content to be at the top of the page. Initially when I clicked the link I immediately saw "sign up to access" on 6/7 of courses. Luckily I know how to use the scroll bar :) Just saying I fly though most of these links and sometimes don't even stop to scroll. HN is an awesome market for your team - it might even deserve it's own offer splash page or something.. ? Keep up the good work.
Partly joking here, I too think this is the wrong type of question to ask. So many times I get approached from people who have the next facebook/twitter/fucking-annoying-I-know nothing idea.. do they ever mention the implementation details? No. It's always about going viral and making millions. What do you end up with? Something as spammy as "honestly.com"
Seriously just find an interesting problem to solve, solve it well and see how you can expand on it. The money will come when you aren't focused on it!
This is strictly business. I would get / create a full contract that immediately clarifies how and when you get your percentage. Also what type of stock is this? I second jaltucher's response.
RiderOfGiraffes is absolutely correct. I often do quite a bit of documentation upfront to make sure the client knows exactly what they are going to get. From wireframes to technical summaries, each is a step in the overall project process (and completely billable). Don't be afraid to shoot down something you think is considered "spec" work such as a bit of UI demonstration or data modeling. They either see your previous experience and trust you or not. Otherwise run away - could be a shitty client.
In answer to your specific case - explain to him that the first deliverable is a "project brief" which summarizes the project and proposed "high-level" solutions. Again - totally billable.
I would also suggest picking up so general programming books, especially focused on OO programming techniques. The "Head First" series is a good place to begin. Once you get more experienced, head on over the Pragmatic Programmers publisher site for some more good reads.
Just an idea - can you integrate what the recommended changes for vehicles are at various mileages? That would be killer and a heck of a way to plan in advance. I know the info is out there, every time I go to get my oil changed they pull up a program for every car and review the recommended updates...
I think this especially helps with older cars. For example my truck has 110K miles on it and I just had some major work done (timing belt and new radiator). As life goes on, I need an easy place to remember what I did so some scammy mechanic doesn't try to lay one on me.
Just some critical advice - you might want to redo your screencast. Not b/c it wasn't informative, but b/c it had no energy. I felt sort of like I watching a coding screencast and wasn't excited to take any action. Just a thought...