Don't chase "profitable" right off the bat. Teach what you know best. If you're from a developed nation, "profit" can be a hard target.
You'll discover more as you go. Don't invest too much time and money at the beginning as well. Start with simple gear and straight forward techniques.
Online courses are created with the mindset that students learn something useful after watching every video, every section, and every course. Niche courses do better on Udemy I believe, "focus strategies for students" would sell well as compared to 'learning strategies" since the later is vague and doesn't attract a specific audience.

I've worked through Odesk and Elance for almost 3 years, for last 9 months I'm working as full time freelancer. A few weeks ago, I found a client who

If you got the cash, just hire a few professional coders. Try to focus on your core competencies instead.
You may learn basics of coding, as that will help bridging the gap between you and your engineering team.
I'm a professional coder, feel free to get in touch to discuss the details of your project.

The freelancer is on the right track, and they should stick with their own stuff.

Git is the latest and coolest software, and SVN is the outdated old one. When you tell SVN that you want to create a new branch of your code to have some fun, it creates a heavy weight dumb carbon copy for you. But Git is intelligent, it won't create a new copy for you instead it will only keep track of the things you're adding/removing/changing with respect to the original sources.
I hope I made the point, for more let's have a telephone call some time :)

Most of the times stand alone publications are made up of biased stuff put together to boost the awesomeness of publisher's products, I believe these cannot bring in a lot of leads.
A blog on the other hand can cover a diverse range of topics, you may put references to your publication and your products inside your blog.
That way, your blog will become more authentic. You can also get others talking about your blog which will eventually bring people to your product catalogue.

You can hire app development freelancers from www.odesk.com and www.elance.com.
I am an app developer myself, and I got profiles on both of these networks, a link is given below:
https://www.odesk.com/users/~012d73aa92fad47188

Please feel free to get in touch to discuss ideas and clarify any confusions, I will be glad to help.

I believe LogMeIn is a good software, RealVNC is another option.

Slowly, patiently, and gradually. Building up a passive income takes a good deal of upfront investment.

They've kept it simple, you don't need to fill up sign up forms and remember your user name. Your GSM SIM card is your identity.
Secondly, they tightly focused on SMS market. Didn't go for multi party video conferencing, screen sharing, and other seemingly cool stuff.