It’s time-intensive, so working with experienced teams can make the process smoother. 

She helps design the rehabs and remodels, while I look at the numbers, do the more labor intensive work, and make sure we stay on track.

Real estate investmnets are capital intensive and if you don't have extra money sitting around to make the emergency repair when it happens you'll find yourself in a terrible position. 

Besides the technical aspects how has it been knowing there is someone living so close and dealing with any potential noise conflicts (loud TV or whatever)?

The police were called due to the noise.

But I’d also buy the $200 5 year warranty.My last/only stackable I bought last year was LG, the combined towers to try to reduce noise, increase ease of use, and presents higher end look.

Don't do any Structural type flips.Reduce the risk and start learning.If the above are to labor intensive, either buy a hill or buy some swamp ground.  

REI is capital intensive.

However, with high rates, the next mortgage would be very expensive, and a vacancy would be intensely expensive with two mortgages.

Keeping it friendly and low intensity is more likely to be successful.I recently offered to completely replace my neighbor's fence next to my rental and they said "No".