Hi Wallace,
It's great to have people like you on board... ambitious, motivated, and ready to learn! Having said this, welcome to Website Babble!
As you are aware, your post raises many important questions that span a lot of the topics discussed in this forum.
I don't think I will attempt to answer all of the questions you raised right now, but I want to provide some direction concerning the beginning phase, i.e. where to start.
You mentioned you have many interests and ideas... that's great, since a lot of people want to make money online, but have no ideas. I don't think you need to start with real estate. Although you may be able to find a unique twist or approach that hasn't been covered before online. So don't exclude it just yet.
Here is what I would do if I were you: I would make a list of about 5 topics (aka niches). Ideally, this is what I would look for in a "topic". 1) I have some interest or knowledge in it, 2) a good size group of people are also interested in it, 3) these people are willing to spend money on it, 4) a sub-group of those people are really passionate or really hungry for something within this topic, 5) I can think of ways to add value to this group of people.
I would start with making that list. It sounds like you have a lot of ideas already, but to help narrow/focus your topic, watch commercials or ads... identify the markets and people that are targeted. I think the most important aspect of focusing a topic is narrowing it down to a group of people.
This is where I would start

Please let me know if you want me to clarify or elaborate on some of those things.
Now, regarding your question about why it could take $500k to $1M for a web start-up. Some of these websites require a lot of programming and databases on the back-end that would require a full-time programmer or two. Some of those companies want to have a physical presence, which means office space, office supplies, administrative assistants, etc. Some of them require manufacturing products, running ads on TV, hire consulting/marketing firms to launch a branding or marketing campaigns, etc.
It really depends on a lot of factors. But the more overhead there is, obviously, the higher the risk... This is why monetizing a website through affiliate marketing carries the least amount of risk since you don't have to carry your own products, fulfill orders, or hire anyone, at least at first.
If you hit a home-run with an affiliate website, then you can move it to establishing a product, hiring people to help, etc.
Sorry I rambled on... but I hope you found some helpful info in my post.
Sherif