Think what might be the advantages and the disadvantages of having partners. 

Naturally there are advantages/disadvantages to both approaches.

If you can capitalize the expense over a longer period of time it sounds like a decent move since it's not a large amount of money. 7 years is a pretty short period of time and at times when it is not rented you will be far more cash-disadvantaged than you already are, since the payment and realistic income are virtually even. 

I am currently a student in college so taking on a mortgage at this time could become a financial burden if I don't find tenants somewhat quicly.I was wondering what advice anyone can offer me on the advantages/disadvantages of purchasing a rental property that has pre-existing tenants.

The fact that you are not a cash buyer is also to your disadvantage in locking up deala, relatively speaking. 

I think is clear enough for everyone that LA market has a lot advantages but also some disadvantages.

Railroad land has quite a few advantages (federally backed so no zoning regulations), although there are quite a few disadvantages as well.One of the biggest disadvantages of railroad land that I have experienced (and this is a very general statement) is that the land is usually not near the people. 

The disadvantage here might be that he has been getting away with this for some time, it will be more difficult to "re train" your tenant at this point...  

I understand the importance in keeping personal and business bank accounts separate, but is there any advantage or disadvantage in keeping them in separate banks?

KICK THEM OUT.Section 8 has its advantages and disadvantages.