He's gonna be complaining about noise from his neighbors who are just walking around.

You could even look at making the 2nd unit into a STR, before permits come in, since STRs are legal here in Vista.We're in Vista close to downtown and love the area (besides the noise from the train).

They can quote the by-laws by song and verse... be it the decoration you tenant hung on the door, or the tenant's inoperative car, or noise violations, etc, etc.I would definitely check into the rules of the HOA.  

I just don't love the noise and hassel she causes in the 8 units we have.

He thinks bad news sells and it’s the best way to make noise and get people to listen to him.

She is looking to move to Florida, and can't sell this home due to:1) She wants top dollar2) The home sits next to a transfer pump station (eyesore)3) It sits on a main road (traffic, noise)4) The community pool is behind the home and visible from the deckThe home is in immaculate condition.

@Victor Nguyen for starting out either is fine if the numbers work, but if you do a duplex I would recommend starting with the a side-by-side duplex the first time you do one rather than a multi-floor building.The reason being is that managing multis (duplexes) with tenants living over each other come with different problems such as noise complaints, and can limit your options accepting pets.

Single-Family Home with a Basement:Pros:Familiar single-family living with potential rental income.Can be a good starter home, quieter living if the basement is well-soundproofed.Potentially lower initial investment compared to a duplex (depending on renovations).Cons:Finding tenants might take longer, especially if the basement isn't a fully formed apartment.You'll be responsible for all maintenance and repairs for both units.Less separation between your living space and the rental unit.Multifamily Duplex:Pros:Clear separation between your living space and the rental unit.Potentially higher rental income with a full, separate unit.Faster tenant search as it's a more traditional rental format.Cons:Might be slightly more expensive upfront than a single-family home with a converted basement.Potential for noise complaints if the duplex isn't well-built.Dealing with potentially two sets of tenants (though vacancy rates are typically lower with duplexes).So, which one to buy first?

Drown out the noise and stay focused - I had alot of people telling me I was crazy 5 years ago when I started. 

Building in a downtown area typically involves privacy fencing the entire site, permits for road blockages, fights with neighbors over port-a-potties, and difficulty with noise ordinances.