Completing cosmetic updates to the interior, painting the whole interior, removing drop ceilings to make the space feel bigger, gutting and renovating one of the bathrooms.

I have almost finished the kitchen remodel as well as the master bathroom remodel.

Not including bathrooms updates though.

If you're also adding plumbing, electrical,  a bathroom and a kitchen then I'd say it's not enough.

They "party" (slamming doors, talking ludly, and throwing up in the bathroom) until 5 am.

Try looking into zillow/Redfin and see what your potential rents you can get near the neighborhood by filtering the bedrooms/bathrooms of the intentional property that you are planning to buy.

I recently found a property on Zillow that looks to be in good condition (built 1940s) and has a finished basement that could be rented out as a Mother-In-Law unit (separate entrance, kitchen, and bathroom) while my partner and I live upstairs.

I live in Phx,az and recently friend of mine sold his bank (ex bank of america) literally as is and profiteed $300k  , he purchased it right out cash last year (I think) and it was in real bad shape in a shady part of town,  before him taking possession of the bank  homeless people where living inside it an using the bathroom anywhere in the building, he put maybe less than $5k in just cleaning it up and just a couple of days sold it.Basically the idea is to find super cheap homes in ****** conditions but the price is so cheap that you could still make profit by selling as is, investing as little as possible..

It is a 3bedroom 1 bathroom house and I am wondering if I should invest in another bathroom or leave it as is. 

I bought a 6 bedroom 4 bathroom home now.... https://www.zillow.com/homedetails/5526-Shiloh-Ln-NE-Cedar-R...Ill be buying another one in a year.