Risk tolerance and streams of income available (and how weak or strong they are) are big factors to size of reserve fund, then add in level of home prices, interest rates and costs of loans to determine how much leverage we're comfortable with.  

I would put up with it all except for the noise, we share a wall, constant banging, slamming, yelling (wife's normal voice is yelling).

Like @Corby Goade I did it backwards of first becoming an investor and many years later becoming an agent, which I totally regret now and feel like an idiot, I just didn't know what I didn't know.If your serious about REI the MOST important thing for you to do is to just do something, anything, just stay engaged, actively doing some forward-moving action, there must be constant forward action no matter how small or big. 

We already went through all this when the tenant signed up nearly a year ago but I don't know the legality of asking such questions after the lease has been signed, even if it was a year ago.Also, with moratoriums on evictions in most states and California being one of the most tenant-friendly states out there, would it be wise of me to have the tenant sign a 3 or 6 month lease and constantly renew it so as to not lock myself into quandary in the event my tenant's situation takes a nasty dive? 

Neither of my tenants got along and I constantly had to be the middle man to disputes and find ways to come to compromises or setting new rules to follow.

Knowing that we were able to help with just 1 month has made the difference in their constant worries and saving us from the hundreds of evictions we would otherwise be faced with an ethical dilemma of doing.

Other factors like presence of hospitals and colleges and are strong economic factors that point towards a steady stream of renters for that area.

I am constantly on the lookout for Zillow listings that pique my interest.

@Tyler Sample There are pros and cons to each, just depends in how passive you want your income stream.

I hear this from customers constantly.