Check out Noble Mortgage, I'm currently doing two refinance loans with them and they have investor friendly approach to things.

I want to best approach these people I'm wondering what happens to those people who go with discount brokerages?

One great approach is to draft into the operating agreement that early exit isn't permitted. 

We respect those who would approach this differently.

After several years of education, preparation, and researching countless markets and strategies, my wife and I finally turned all the theory into reality and bought our first rental property in 2020.

Maybe approach it backwards......ask them how much more rent they'd be willing to pay for an extra bath?

If were to approach a developer to build a multifamily property and the cost would be $2million, how do I determine what the post construction value (for cash out refinance) would be once its filled with tenants.

If were to approach a developer to build a multifamily property and the cost would be $2million, how do I determine what the post construction value (for cash out refinance) would be once its filled with tenants.

How do people typically approach buying a second home like this if they want to keep the first one and rent it out.

You may want to call a lender or two and understand how they would estimate the value as you may get a different value based on the approach.