Also, your total returns go down without any leverage because you lose the multiplier effect of appreciation.Now, to answer your question.

@Phillip Austin I self-manage my properties including some where I do rent by room as a primary strategy, and it is very effective if done well with good screening in place.The difference is starting with shorter leases for me. 

I’m about to be 29 and I’m hoping this really takes effect in my life in my 40’s.

Most come out ahead over an extended period of time by buying better quality assets where they perhaps have to leave some capital in the property but find themselves able to sell for real gains or refinance out appreciated equity and scale more effectively that way. 

In your opinion, what is the most effective way to establish an LLC? 

I haven't seen any statistics to this effect and I don't think any has necessarily been compiled but I bet I wouldn't exaggerate if I state that 95% of the value of real estate in Southern Spain or at least the province of Andalucia is in the Costa del Sol.

Any tips on targeted marketing, effective lead generation, or even some "outside-the-box" tactics?

Start small, network with other investors, and use tools like BiggerPockets calculators to analyze deals effectively.

You don’t need a judgement, but not sure how effective it would be:   https://www.rentrecoveryservic...

How can I effectively gather evidence to support my eviction case, such as documenting the disturbances, obtaining witness statements from other tenants, and documenting the tenant's interactions with my son?