Preface: I come from a family of landlords. My grandparents built a small fortune in real estate through the '60s-'80. My uncles all dabbled in the arena. I am not unfamiliar with the trials and tribulations of this path to prosperity, but to say I am anything more than a novice would be disingenuous.

Why am I doing this? After faithfully maxing out in my 401k and IRA for the better part of 8-years, I realized the "Returns" portion of my accounts were full of shit. When I considered the difference between my "Account Growth" vs. "What the financial institution actually doing with my money", it was literally the difference between 16% (a big fat fucking lie based on my continued contribution + employer match + minimal growth) and 2% (actual 12-month account performance).
I came to the realization that the only people getting rich were the fund managers and financial institutions managing my money.

How to get start-up capital? Well, despite taking a big fat dump on the entire 401k scam as stated above, I actually took out a loan from my 401k to get started. The limit on this is 50% of your account balance up to $50,000 maximum, which is then paid back into your own account at 4.25% interest. The actual number needed to get started will vary case-by-case. I pulled out $50k. There are other methods but this is how I did it.

Selecting a building: Look for multi-family properties. The more units the better within your price range. In my area, there are things called "Rooming Houses". These buildings have single room dwellings, no kitchen facility and a communal bathroom or two. I was able to buy a six unit building for $90,000($15k/unit).
Comparatively, a single family row-homes on this same block are going for $40k-60k.

The Maths:
Purchase price: $90,000
Down payment: $22,500 (25%)
Check written at settlement: ~$27,000
Monthly mortgage payment: $420 (Unplanned and true)
Rent collected: $400 x5 units, $300 x1 unit = $2300 monthly
Utilities paid for by landlord: ~$300/month
Insurance: $604 annually
So basically the building, when fully occupied costs me about $420 + $300 + $60 (mortgage, utilities, insurance, maintenance) per month or roughly $800. I collect $2300. That means I have a liquid $1500 a month before taxes.
Of that $1500, subtract $400 for whatever random maintenance bullshit happens. This is a gross over-estimate. Deal with it.
That's $13,200 annual cashflow before taxes. That's a 48% cash-on-cash return. ($13,200 / $27,000)

Landlording: I would be lying to you if I said this was completely hands-off. I work 40-60 hours a week for an actual employer and an additional 10-20 hours in direct support of this building. 10-20 hours doing what? Calling contractors for things outside my of ability like getting the roof replaced (seller paid for it as part of the purchase contract), getting an exterminator to spray for bed bugs in one of the units, replacing troublesome deadbolts, rewiring a junction box, patching concrete and digging a 30' long trench to run a down spout extension away from the foundation to prevent water intrusion into the basement, installing deadbolts to increase security, talking to the tenants about their concerns and delivering notices about upcoming inspections or intrusive work.
Property Management companies will handle the bulk of the work for you, if you choose, but they do so for 1) a small fee, typically between 5-15%, and 2) they use their own contractor contacts, typically on a "pass-thru" zero-markup kind of deal, but actual contractors in my area charge about $60/h. I have a local handyman that works for $15-20/h. That ditch that was dug last week? He did that. I helped with the PVC, down spout attachment and backfilling. For $50 in materials and $100 in labor, we knocked the job out for far less than an actual contractor would have. These are your profit margins. I don't mind physical labor.

A Word of Caution: The tenants in this socioeconomic group are often mentally and/or physically challenged and are very likely addicted to one thing or another. I carry a concealed pistol with me daily. These buildings are typically in poorer areas. Situational awareness and the ability to actively defend yourself is paramount. Yes, there is a very real risk in these areas but they are also the most lucrative for someone in a position like mine.

Moving Forward: With one property under my belt currently, I am moving on a second building with seven units that generates $3000/monthly for about $135k. This has the same kind of tenants but this building is in better repair. The profit margin in about the same ~$1100-1500 per month.
I am not currently using a management company but I did sit down with one last week. Because I have other arrangements for rent collection, they agreed to take on the responsibility for 4%. Once I settle on this second property and spend a few months getting things up to my standard, I will be turning control over to the property managers. I will still be involved but less directly available to the tenants.

Investors: I didn't advertise. The day I closed on my first property, I posted a picture on Facebook with my realtor and I shaking hands. That was it. Two weeks later I had access to over $100,000 in cash from people who were similarly dissatisfied with the market and wanted me to makes moves with their money. I drew up a contract that literally states, "I promise, guarantee and will be held liable for nothing. You are surrendering this money to me because you trust I will act with your interest in mind."

Final Words: I command a handsome wage at my full-time job. This real estate venture is simply a means to an end. I don't want to work at my current job for another 20+ years before I retire with the standard pension/buyout. I want more. I want to enjoy a better quality of life, to generate actual wealth, and I'm willing to work for it. Hell, I'm willing to sweat and bleed for it. I'm blazing a trail and people are getting behind me. The possibility of failure is very real but it's better than never trying.