I had to do some work on one of the rented houses so far (by insulating and reinforcing the structure), and now I will focus on rehabilitating the 3rd house for I can start receiving some cash flow.

This will help clarify and reinforce what you are reading.

To just reinforce the message here we usually don't use a conventional loan to BUY a property. 

@Horacio Gutierrez just to reinforce above you can certainly buy another primary home.  

Many waste drains go under the joists, but if you have to go through them and are worried about weakening them, then just reinforce them by screwing a 2' to 3' length of joist board to the side of each joist you have to go through.   

Luckily there are tools that can help you to actually build a single listing and syndicates it to 10+ major listing sites, allows you to schedule showings, provides you with super thorough tenant screening options, online digital leases which can be customized and help you by breaking out those fees, automated maintenance tracking, and fast rent collection which also offers your tenants the ability to report their positive on-time payments to the major credit bureaus; just another positive reinforcement/added incentive to get them to make those payments on time).

I will say, it could be worth considering a shot at an actual software solution built for DIY landlords (1 - 25 units) that helps you to automate your own rental process (ie. compared to other tools, one that helps you to actually build a single listing and syndicates it to 10+ major listing sites, allows you to schedule showings, provides you with super thorough tenant screening options, online digital leases which can be customized and help you by breaking out those fees, automated maintenance tracking, and fast rent collection which also offers your tenants the ability to report their positive on-time payments to the major credit bureaus; just another positive reinforcement/added incentive to get them to make those payments on time).

Thanks for reinforcing my learning and helping others. 

Sewer Lateral Ordinance Sidewalk OrdinanceRental OrdinanceFIRPTAThe reputation of the inspectors the Seller chose to do pre-inspection Test Holes (if applicable) Seismic reinforcement workResponsibility removing contingenciesNo matter who you work with, make sure you get a clear explanation of each of these as they are very important here in Oakland. 

Friends, family and co-workers are the easiest starting point for initial investments and when coupled with expert partner information/resources, security and credibility are reinforced.