The ability to effectively self manage would depend on the scale you are trying to buy. 

The streamlined process and strong market demand allowed Partner Driven and Nathan Ward to capitalize on a quick-turn opportunity, demonstrating the effectiveness of their partnership.

Again, the BiggerPockets store has some books on this topic, or you can learn about it by watching podcasts, reading blogs, and interacting on the forum.

I share tons of free tips on my instagram @ericaoohdesigns and you can also check out my Bigger Pockets podcast episode (933: https://www.biggerpockets.com/blog/real-estate-933) where I share my exact "Designing for Dollars" formula.

This would imply AA has an effective tax rate of ~3.5% for an investment property 

This would effectively cover your mortgage and significantly reduce your living expenses.

What tips and techniques have you found most effective in increasing rental income and property value?

The conversation covers issues like the impact on property values, tenant rights, and the broader effects on the real estate market. 

I recently completed one on a multifamily property and found it to be a cost-effective approach.That said, there are a couple of additional factors to consider beyond the code differences between a garage conversion and new construction:Coastal Overlay Zones – If your property is in a coastal overlay, building a ground-up ADU may require Coastal Commission review, which can add time and complexity to the process.

If your 401K is with your current employer, it is (effectively) impossible to make it an SDIRA.