Then, jump on your property manager for allowing this situation to happen.  

Can anyone recommend lenders who will allow for getting a mortgage in the name of an LLC for purchasing a mixed use building in Philadelphia.

In general the IRS does not allow married couples to deduct home mortgage interest on loan balances above $1,000,000 ($500,000 for single).  

They also have a free service called rentalizer, that allows you to enter any address and if they have info for it, they can guesstimate how much you may get as a AirBnB landlord.There are a lot more sources and blogs dedicated to this, so a search on google for "airbnb best markets" can give more details.Hope this helps!

Assuming you live in Sacramento, CA and your lease allows for it, I would be airBnb'ing the sh*t out of that apartment.

Account Closed rolling over your $75,000 in your 401(k) plan into a Self-Directed IRA would allow you to avoid the "dummy tax" and let you use the funds to purchase real estate.

In my town, we have what's effectively considered "allowed non-conforming properties" which are exactly like you discussed...multi-unit buildings in single family zones, etc because of grandfathering.

I don't know if this is allowed... but I just bought a 63k house in IL and used Busey Bank.

RT1 allows for up to 2-family properties.

This would allow you to defer the taxes on the sale whether you treat it as your personal residence or an investment property.