Do you need to restretch it when the unit is occupied and did she know you were going to do it? 

If it's just you or just you and a partner, your best bet when looking to house hack a multifamily is to look for uneven unit sizes.

I understand that I should have a separate bank account from my personal checking/savings, but based on my research, this first deal won't necessarily provide cashflow with me living in one of the units (it will when I move out).

I've done both a HELOC and a cash out refinance on my current house to buy my 9 units and it may not be the most efficient way to purchase but it has allowed me to own 2.5 million in real estate and have 500k in equity that will grow at 3% or $75k a year with normal inflation.   

I think I'm an accidental owner of a few rental units in the metro-Atlanta area.

I was looking at an apartment building 100 units for 17 million with a 10 cap. 

Where you are building your wealth is the appreciation and don't forget rents tend to go up over time so as time goes on the unit gets more profitable from a cash flow perspective. 

My HOA has said they're not responsible, but I have been told that the issue won't be solved unless all the units (less than 10 total), are sealed. 

The studio has large windows on both sides of the unit so i do not want to loose any of that natural light, and I am thinking of eitherA - Doing a full glass partition wall with glass door, with smart glass that can frost to create privacy when in use and allow sunlight when not in use to both sides of the apartmentorB - Doing a higher end full wall foldable partition on a track that closes the whole new "room" into a bedroom but can close back up and fold away to make it a studio again if not in use.Thanks for your input

House hacking means living in the place you are fixing up or let's say you have a triplex and you live in one unit and rent out the other two.