However, I think on a residential scale, a good, reputable builder, etc generally has enough steady work.

My father and brother have both succeeded in flipping and single family rentals on a small scale.

At this point though, I need more scale and want to move into apartment buildings.

A property scale-up success story and a buyer's agent success story to boot!  

Generally speaking, MF has more turnover than SFR but you don't get the fast scaling of income in SFR.

If it destroys your life financially if the worst was too happen, the deal is too big and you need to scale back.Once your comfortable with doing deals, those items won't even be a concern anymore.

That product has to A) fill a need B) The need has to be large enough that the target market can generate sufficient scale to generate profits and C) has to be either difficult to replicate by competitors or protected by intellectual property rights.

Then I plotted my map large scale and began adding information.

Buildings need maintenance, and that cost doesn't scale down with a lower income.

I have long been searching for something I can do on the side, without much money, while holding a job, and preferably something that could be scaled up to provide primary income in the future.